Why not automate the whole process like we did?
OutWit hub for firefox. You can design price scrape profiles for each of your competitors by setting up a profile, and set them to run early hours of every morning. It kicks out a csv file. Line those prices up against your own on an excel template, red highlights anyone cheaper, you review the price.
You can even dump the scraped data to an online db and project competitors prices live into your pages, or in theory auto update your own prices... I'd be careful with that last method though, if you did it to me I would be more than capable of feeding you dummy data
Probably best to just scrape and go through prices manually just in case they get wind and sting you with silly data. Or safer still, if they all use google base, scrape from there as the data is guaranteed to be what they display to the general public, and not just your IP.