I've been looking for a cart that I could tow behind my bike so our dog Maynard could go along when we ride our bikes while camping. We hate to leave him behind. Found this deal at Target for $94.
http://www.target.com/Quick-%E2%80%98n-EZ-Bike-Trailer/dp/B00006JHVN/sr=1-1/qid=1247608820/ref=sr_1_1/180-2654668-1096913?ie=UTF8&search-alias=tgt-index&frombrowse=0&index=target&rh=k%3Abike%20instep&page=1 (//%22http://www.target.com/Quick-%E2%80%98n-EZ-Bike-Trailer/dp/B00006JHVN/sr=1-1/qid=1247608820/ref=sr_1_1/180-2654668-1096913?ie=UTF8&search-alias=tgt-index&frombrowse=0&index=target&rh=k%3Abike%20instep&page=1%22)
It's meant to be a two baby stroller, but I easily modified it to serve as a pet carrier. The best price for a pet bike cart I've seen is almost twice as much.