I am going to hook up two of them - Amazon.com is selling a refurb. Logitech Quick Cam Express USB for approx. $22.00.
They're readily availible on Ebay as well - The same refurb. camera is up for Dutch auction (several) but I wouldn't go any higher than $18.00 on them - or else just order them from Amazon...
They're cheap enough to experiment with - if it doesn't work, I was thinking of going with a CCD camera - if I could find one cheap enough to mess around with.
Hope this helps!