I worked on this, it was called Milo.com. we had crazy scraping and xml/csv feed ingestion. It was a terribly difficult business because most retailers hated us. ebay bought it and eventually killed it.
Funnily enough though Best Buy loved us and provided real time data via API and daily CSV data dumps just for us. They were like that, along with Toys R Us and AutoZone. Most others hated us, including Guitar Center after we accidentally DDOSed their web site with our scrapers.