I used to use b&h photo. They'll match prices but you sometimes have to haggle over the phone.
I don't think you can beat amazon for hassle free and low prices. I don't order from them though when you have to buy through a third party. However I've ordered several canon cameras from amazon directly and there's been no problem, lower prices than any camera store and fast, free delivery.
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.