The DMG describes the maximum value of any item that a town of any given size may have available for sale.
It also describes how much cash any given town is likely to have available for buying stuff from PCs or whatever. I don't know the page numbers for the 3.5 DMG, but in the 3.0 DMG it's page 137 in the Adventures chapter, under Generating Towns.
Community Wealth And Population describes that the amount of ready cash in a community is half the town's GP Limit (like 40 GP for a thorp, which would be 20 when halved), multiplied by one-tenth the population. So for a thorp of 40 people, it would be 40/2=20, 40/10=4, 20x4=80, or 80 gp. So a little thorp like that could only afford to buy up to 80 gp of loot from a group of adventurers. How long it takes for the community to convert that loot back into coinage or something through trade is up the DM.
