I'm not sure how cheap they are, but when I was at TCEA I saw the most incredible cameras, computers and other educational manipulatives available from RM Education. The cameras are actually in the shape of laser guns. These things would probably be better for elementary and middle school students than high school students.
I would second newegg for tech stuff. When buying for myself I usually check out reviews on www.cnet.com and then go to newegg to look at prices. www.Buy.com and www.buydig.com are also good ones. Buydig specializes in cameras. Depends on where you're shipping to, though.