Here is a system I came up with after reading this thread. I'm not going to argue over whether it should have existed or not but:

You can create a very generic and generalised cost system using the availability of items:

Avail Cost (tg)

Dark Heresy Availability levels

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Abundant - 10+1D10

Plentiful - 20+2D10

Common - 40+3D10

Average - 80+4D10

Scarce - 120+5D10

Rare - 240+6D10

Very Rare - 480+7D10

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Rogue Trader Availability levels

Ubiquitous - Virtually free

These should all be GM discretion only. If legitimately buying something with this availability the GM should modify it as much as they deem appropriate.

Extremely Rare - 100,000+1D10x100

Near Unique - 1,000,000+1D10x1000

Unique - 100,000,000+1D10x10,000

Modifiers:

Bolt: Add 1D10x10

Plasma: Add 1D5x1000

Melta: Add 1D5x1000

Xenos: Add 1D10x1000

Power wpn: Add 1D5x1000

Power armour: Add 1D10x1000

Primitive: 1/2 cost

Pistol: Add 1D10x10

Heavy: Add 1D10x100

I'm sure you could go into more detail and this won't represent everything perfectly. Obviously if a similar weapon already exists it shouldn't cost too much more or less than that.

The thing to remember is to look at the availability and compare it to an already priced object of the same type. If you are looking at the availability of a Plasma Pistol (Ryza) (Very Rare) and compare it to the cost of the very rare plasma pistol from the DH book, then it shouldn't have too much of a cost difference, it would cost more though because it's better.

You could simply look at the item's stats and availability, find a similar one with the same availability and then reduce or increase the cost relative to its quality (ie if it is worse reduce the cost by X, if it is better increase the cost by Y).

This isn't a substitute for proper costs, but the availability should give your a very rough idea of how expensive the object should cost.

Hellebore

@ Hellebore

Thanks, that will help me flesh out some costs that I can then set for a list. I had a good ideá about the value since most items are the same as in DH, but wanted an official one. At least now I can use your guide to get a fairly balanced sum for the items.

Keep in mind that non armour/weapon items may not follow very closely with this. I don't think ammunition needs to be costed because most of it already is. Anything else will be xenos tech.

Hellebore

I seem to recall that someone on the development/playtest team posted that a Stormbolter was about...1250 thrones