Product Shopping engine search algorithm

Using xml data (Product name, price, condition:new, and possibly upc) from my my volusions store, I would like to set up an algorithm that searches the following shopping engines and reports vendors with a lower price then mine (with url to listing)- Should be able to run search against less than 3000 products twice a day. Search Engines- Google Shopping Ebay Amazon Bing Nextag Shopzilla [login to view URL]