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It probably depends on how the stores provide their data. I'm trying something similar with Amazon.com, Audible.com and a few other companies that I'm an affiliate with that provide xml feeds of their latest products & prices.
The feeds get entered into the RSSC module developed by Happy Linux. It creates a searchable database - problem is that the module is a kind of picky about what feeds it accepts. Works ok with most xml, rss and rdf feeds, but not all. And the developer isn't very good at answering questions on his site. Basically a good module - when it works.
gestroud