XML Standard for exchanging grocery prices

Hello everyone,

For an academic project, I am developing a program that basically 
functions like a comparison shopping tool. It needs to compare the 
prices of items from several stores, and display the stores that are the 
closest to the person.

In order to get this to work, I need the price data for various stores. 
I first thought that since Web Services were such a big hype, I would 
have no trouble getting such information. However this proved much 
harder, and I couldn't find any resources.

Are there any standard XML standards for sharing this kind of price 
information (perhaps even just for grocery-like items)? How would I go 
about discovering web services for this purpose?

Any help would be greatly appreciated, as I have somewhat hit the wall..

Thanks,
  Berk Birand