You can get agricultural market data easily enough. You'd have to figure out transport costs (which could be done using a heuristic and google maps).

The next step is getting them to upload the prices they get, then filtering that (as buyers may try to destroy the system). But that's for version 2.

A quick google and I found this: http://www.guardian.co.uk/katine/katine-chronicles-blog/2010....

This comment is probably the most insightful thing on the page: http://www.guardian.co.uk/discussion/comment-permalink/71754...

Esoko http://www.esoko.com/ is a good example. I've seen these in action in various places and I've been skeptical about how much value they actually bring to the table. Price information actually disperses pretty quickly, and for most commodities prices aren't that volatile. In the markets where wholesalers sell vegetables, you see people getting screwed by the middlemen, but basically it's because these middlemen control the marketplace, not because of lack of information.