AK47 (C/V) --$100
SKS (C/V) --$250
All else being equal, you might as well buy the AK47 if you're going to stock your militia's armory.
Which leads into another question: if you are buying weapons on the open market, say, in Krakow, how many would be available of a type, assuming average success in rolls? I realize this is at the pleasure of the GM, but what should be the limiting factors in units when the item's availability is a given. One? Five? A dozen? As many as they have cash for? The last is highly unlikely considering the somewhat limited contents of the caches of the marauders in FCOK.
I guess a die roll here and there will help. Scrounging, Gunsmithing, and other skill levels could help the player sort out the wheat from the chaff--identifying weapons that would require major repair or are actually inoperable. And other givens are the rule-defined conditions (Rare, Scarce, Common, Very Common) and the locale (major city, city, town, village, open).
Sorry for thinking out loud, but I often try to anticipate problems before I am confronted with them.