Assumptions:
-Extended Magazine costs 10 more per magazine, increasing ammo cost. Solid Slugs is 1 for 15.
-Hellgun Capacitors (the smaller kind) cost 50 for one belt pack, for any hellgun style.
-You can silence/suppress Shotguns, regardless of what the rules say, cause that is possible, but difficult, in real life, and apparently you can suppress large caliber hunting/sniper rifles in this game, too.
-Extended Magazines can be combined with Duplus Clips, but not a Fire Selector (you choose which of the options to get more ammo on your gun).
-Only doing one full ammunition load for the example weapons, under the assumption that if you can buy one full ammunition load, you can get more ammo.
-You can't Duplus or Extended Magazine a Hellgun Capacitor.
-You don't want to put lots of things, like melee attachments, knives, or Exterminators, at the end of a sniper rifle (anything with at least 150 range and Accurate).
-Expander Rounds cost 5 for 6.
-You can upgrade an existing integrated melee weapon on a firearm to a mono variant for the mono price.
-You can put duplus clips in a Hellgun that can fire normal charge packs.
-Maglev Impeller Upgrade costs 150, and puts coils around the barrel of a weapon, making it a hybrid energy coilgun/solid penetrator weapon.
-Hellguns that can use normal charge packs get no benefit from Overcharge packs.
-The full sized backpack ammo pack is 100, and gives between 120-150 for most hellguns, and 200 for solid penetrator and boltguns.
-A Photo Sight costs 200, and can be put on top of a Telescopic Sight, but you can only benefit from one at a time.
-You can benefit from an optical sight and a red dot at the same time.
-An ammo backpack for a weapon that uses both electric (as in laser charge pack) and solid penetrating ammunition has half the total number of each that it would normally have, unless the chemical propulsion of the bullets is removed (like for a coilgun, ie, maglev impeler).
-You are not generally getting these things all at once; you are spending time and effort slowly getting the various modifications over time, and then putting them on your weapon with the appropriate skill use (tech-use, trade technomat, trade armourer).





*Up to Common, and under 100 Thrones:

Steadholder Lever Gun (60) + Silencer (10) + Bullets (.3/clip). Total: 70.3

or

Talon mk III Autopistol (70) + 30 round mag option + Silencer (10) + Bullets (1.5/clip). Total: 81.5

*Up to Average, under 150 Thrones:

Armageddon pattern Autogun (100) + Telescopic Sight (35) + Silencer (10) + Bullets (.75/clip). Total: 145.75

or:

Anoxis Pattern Stingray Rifle (100) + Melee Attachment (25) + Knife (5) + Basic Charge Pack (15/pack). Total: 145.

*Up to Average, Under 350 Thrones:

Skitarii Vanaheim Assault Shotgun (300) + Solid Slugs (1/clip) + Telescopic Sight (35).  Total: 336.

*Up to Scarce, Under 350 Thrones:

Death Light Sollex Lasgun (if you can make it to Magnogorsk) 250 + Telescopic Sight (35) + Melee Attachment (5) + Knife (5) + Basic Charge Pack (15/pack, 2 for 30) + Duplus Clips (10). Total: 335

or:

Minerva-Aegis Las Carbine (150) + Melee Attachment (5) + Combat Knife (40) w/Mono Upgrade (40) + Telescopic Sight (35) + Red Dot Laser (50) + Basic Overcharge Pack (15/pack). Total: 335.

*Up to Rare, Under 600 Thrones:

Voss Hellgun (180) + Basic charge packs (15/pack, two for 30) + Duplex Ammo Clips (10) + Melee Attachment 5 + Combat Knife 40 w/Mono Upgrade 40 + Telescopic Sight 35 + Auxiliary Grenade Launcher (250) + Gunmetal Solid mk III grenade (10). Total: 600.

or:

*D'Laku Crusade Hellgun (if you can make it to the Lathes) (500) + Basic charge packs (15/pack) + Telescopic Sight (35) + Red dot Laser (50). Total: 600.

or

Skitarii Vanaheim Assault Shotgun (300) + Solid Slugs (1.2/clip, for 2.4) + Silencer (10) + Extended Magazine (10, x2 for 20) + Duplus Clips (10) + Telescopic Sight (35) + Mono Upgrade for existing bayonet (40) + Exterminator (35). Total: 452.4.

*Up to Very Rare, Under 1000 Thrones

D'Laku Crusade Hellgun (300) + Hellgun Capacitor (50) + Telescopic Sight (35) + Red dot laser (50)+ Melee Attachment (5) + Combat Knife (40) with Mono Upgrade (40) + Auxilary Grenade Launcher (250) + Inferno Thermal Grenade (60) + Exterminator (35). Total: 905

or

Pax Factorem Rifle (750) + Expander Rounds (5 for 6, x2 for 12) + Extended Magazine (20) + Duplus Ammo Clips (10) + Silencer (10) + Telescopic Sight (35) + Red Dot Laser (50).  Total: 887.

or

Skitarii Vanaheim Assault Shotgun (300) + Solid Slugs (6.67 for 100) + Silencer (10) + Ammo Backpack (100) + Telescopic Sight (35) + Mono Upgrade for existing bayonet (40) + Exterminator (35) + Auxiliary Grenade Launcher (250) + Inferno Thermal Grenade (60) + Maglev Impeller (150). Total: 986.67.

*Up to Very Rare, Under 1500 Thrones.

*Pax Factorem Rifle (750) + Ammo Backpack (100) + Expander Rounds (166.67) + Silencer (10) + Photo Sight (200) + Telescopic Sight (35) + Red Dot Laser (50).  Total: 1311.67

*Good Quality (600) D'Laku Crusade Hellgun (300) + Ammo Backpack (100) + Telescopic Sight (35) + Red dot laser (50)+ Melee Attachment (5) + Combat Knife (40) with Mono Upgrade (40) + Auxiliary Grenade Launcher (250) + Thermal Grenade (60).  Total: 1480.

*Good Quailty (600) Skitarii Vanaheim Assault Shotgun (300) + Ammo Backpack (100) + Solid Slugs (6.67 for 100) + Silencer (10) + Telescopic Sight (35) + Mono Upgrade for existing bayonet (40) + Exterminator (35) + Maglev Impeller (150) + Photo Sight (200).  Total: 1476.67.

*Scourge Boltgun (650) + Bolt Shells (24, at 16 each, for 384) + Telescopic Sight (35) + Exterminator (35) + Auxiliary Grenade Launcher (250) + Thermal Grenade (60) + Red Dot Laser (50).  Total: 1464.



Note: Basically, Inferno Thermal Grenades are really really nice all purpose grenades, and getting an auxiliary grenade launcher is very good, and you generally want full auto capable weapons for the +20 to hit in Dark Heresy. I would get everyone Dlaku Crusade pattern Hellguns with lots of stuff added to them; use the Thermal grenades for things that the pen 4 isn't good enough for.

Also, consider using carbines with the Pistol Grip, like the Minerva-Aegis Las Carbine. Use that with a Synford Lockshield, and Carapace Armor. Good Carapace Armor lasts longer on a single charge than power armor (and there are addons to make it vac-sealed, too!), and the Lockshield gets +4 to armor to a lot of areas, and a carbine with a pistol grip can very easily be mounted in the firing port to get the full range, even with one hand. See if you can get a laser backpack that counts as a large scale overcharge pack (or get someone to overcharge it), to go with the Carbine!

A very good dedicated laspistol is the Voss Hellpistol. It is a laspistol that uses standard laspistol charge packs (cheap!), and gets good damage and penetration with those. Get one customized to increase the speed of reloading, and get a bunch of duplus laspistol charge packs, and a bunch of other customizations for the thing.

See if you can get a weapon that counts as balanced monosword, shock swords (with the armored hilt having a punching option and tie into the shock, and have duelist's grips and tox despensers. This lets you:

-Use the hilt to do a low damage bludgeoning, shock attack (think the officer's cutlass as a base), for nonlethal
-Use the blade for a low penetration shock attack
-Use the blade for a higher penetration mono attack (silent)
-Use the blade for a higher penetration mono attack with toxic (silent)
-Be very good at parrying, what with mono, balanced and duelist's grip. If there is one dedicated meleeist in the group, get them a Lathe version of the above (or maybe a Power Weapon version; it depends on how subtle they want to be), to resist damaging by power weaponry.

Basically, it looks to me that Boltguns aren't even remotely worth it! Ammo is just too absurdly expensive.  If you want anti-armor, get a weapon with an auxiliary grenade launcher, and put a krak or plasma or inferno thermal grenade in it!

Unfortunately there is a huge drawback to hellguns and backpacks. They weight a lot. Hellgun + backpack with ammo for 150 shots weights about 20kg. Light carapace about 15, and all those upgrades are pretty heavy. If you are not guardsmen or Tech-Priest, you can reach your carrying limit very fast. 

Oh and I allow my players to buy "real" hellguns like Lucis-pattern hellgun for about 700 thrones. Other weapons from RT too if they like. They are not much better than boltguns, so I don't think they are OP. 

700 thrones is way too cheap, I found one of the best compendiums/adding stuff from RT is the Macharian Handbook, it fixes a lot of stuff and provides sane prices on several items

Note that Lucius pattern hellgun does not have in-built targeter like Cadian pattern from Ascension and Macharian Handbook. They priced hellgun with targeter on 2,700 thrones. Doing this with separately bought targeter and "normal" hellgun with my pricing would be 2,925.

Cheers!

The problem is more that two different Hellguns exist in 40k canon by TT, the classic Hellgun (S3 of Lasgun, AP5 to punch through Flak armor) was in 40k IG Codex for up to 4e, in the 5e codex they changed to "Hot-Shot Lasguns" with a much shorter range, but AP3 (enough to punch through power armor). Most of the hellgun variants below fall into the classic hellgun (lasgun with a bit more OOMPH) OR the new Hotshot lasgun (shorter range, but can punch through power armor).

The lucius hellgun has the best of the Hotshot lasgun (pen 7) but with no drawbacks (shorter range). It becomes a no brainer, no drawbacks, all the benefits. While I may not agree with the version in the handbook, at least it is expensive enough to make it harder to purchase (like a hellgun should)

IH

Hellgun 110m S/3/–  1d10+4 Pen 3 with 40 shots (3 Full Reload, 6 kg, Rare and 180 Thrones)

RT

Hellgun (Lucius) 110m S/3/– 1d10+4 Pen 7 with 30 shots (2 Full Reload, 6 kg, Rare)

ASCENSION

Hellgun (Cadian) 50m S/3/– 1d10+4 Pen 7  with 30 shots (2 Full Reload, 6 kg, Rare)

ONLY WAR

Hotshot Lasgun 60m S/3/- 1d10+4 Pen 7 (2 Full Rld, 6kg, Rare)

Macharian Handbook

Hellgun (Cadian) 110m S/3/- 1d10+4 Pen 7 with 30 shots (2 Full Reload, 6 kg, Rare and 2,700 Thrones)

Note: Both the Ascension and Macharian Handbook Hellguns have targeters built in

Generally, I use these stats as the main types of hellguns:

VOSS Hellgun 110m S/3/–  1d10+4 Pen 3 with 40 shots (3 Full Reload, 6 kg, Rare and 180 Thrones) (can also use normal lasgun packs, gets 15 shots from those)

D'LAKU CRUSADE Hellgun 100m S/3/5 1d10+3E Pen 4 40 shots (2 full reload, 10kg, Very Rare unless at lathes where it is scarce, 500 thrones) (can also use normal lasgun packs, 12 shots from those)

LUCIUS Hellgun 110m S/3/– 1d10+4 Pen 7 with 30 shots (2 Full Reload, 6 kg, Rare), 2,700 thrones (presumed)

CADIAN Hellgun 50m S/3/– 1d10+4 Pen 7  with 30 shots (2 Full Reload, 6 kg, Rare) Also has built in targeters

Macharian Handbook is fanon, fyi.  It's where I got the cost for the Lucius… which isn't described in canon that I can find.

What about hellpistols?

I know it is fanmade, it is also very well done, adds in a lot of missing stuff and minor fixes/tweaks. My main issue is that the Lucius pattern hellgun seems to take the best of the old codex hellgun, with the best of the new codex hotshotlasgun, making a sort of superior weapon with no downsides (at least, no more than a normal hellgun)

Well they all seem roughly equal to me.  The Cadian one (which I view is equal to the Hotshot elsewhere) is better than the Lucius for certain uses because you get a Targeter craaazy cheap in the thing, and the Lucius doesn't have a Targeter.

Hellpistols:

Voss Hellpistol 35m, S/2/-, 1d10+3E, pen 3, clip 20, rld 2 full, 4kg, 140 thrones, rare, can use normal pistol charge packs, gets 7 shots a pack

Cadian Hellpistol 20m, S/2/-, 1d10+4e, pen 7, clip 40, rld 2 full, 4 kg, rare, has built in targeter

Lucius Hellpistol 35m, S/2/-, 1d10+4e, pen 7, clip 40, rld 2 full, 4kg, rare, implied 2500 thrones

4e IG Codex interpretation gives 110m 1d10+4 Pen 3

5e IG Codex interpreation gives 50m 1d10+4 Pen 7

The lucius pattern from RT (and all others based off of it) came out in between codices, so got a bit messed up in its development having the long range of a hellgun (110m) and the penetration of a hotshot lasgun (Pen 7),which is my problem, it has no downside, nothing in at all. But all the upsides of the both codices patterns

Edit: Ignore

Compare Lucius Hellgun to normal Boltgun, and tell me why it should be so expensive?

Range 50m is not that big downside. Most fights happen at closer ranges. 

Guys from Macharian Handbook, took Lucius hellguns and strapped targeters on them, making Cadian-Lucius hybrid, and they priced them at 2700 and 2500. 

Lucius Hellguns are 110m range though