Does anybody know if there is somewhere a rule concerning the creation of blackpowder?

Gunpowder shots are too expensive.

Making a gunpowder power should be cheaper than an arrow if the ingredients are not too rare.

I understand perfectly that just a few specialized alchemist or dwarf/imperial chemist engineer are trained to do it but what could be the price if you buy it in a dwarven stronghold or in Nuln?

And if you manage to learn (perhaps your're a dwarf gunner or similar) the creation's method what could be the cost to make it?

Blackpowder weapons are just slightly better than crossbow but considering the misfire risk they are alredy balanced enought without adding a unaffordable cost.

Well, the fact is that

a) The materials are not common

b) It requires specialized knowledge to create

c) It is not mass-produced, and thus is created by hand

d) The crafting of blackpowder weapons, including ammo, is pretty strictly controlled by Guilds and Dwarfs.

All of these contribute to black powder weapons and ammo being expensive. Really, unless you are a member of the Imperial government, or potentially a dwarf engineer, black powder weapons are essentially strictly a luxury/status item indicating wealth. They are used by nobles, essentially.

Don't forget making it is dangerous.

I mean, the guys making charcoal have to live way out in the woods so they don't blow up the town, and black powder is only worse.