web based app comparing shopping networks

We need someone to write a program that compares pricing from two shopping networks using advanced lexical analysis to identify similar products between the networks and in turn return the prices and calculate the differences between the two. We will need to be able to apply filters such as percentage differences between the prices. For example we can say show all products that are 15% less on this site, etc. We will also need an email or rss alert system when triggered by certain thresholds. More details will be discussed with the potential contractors.