There is a Baja reaction on your local craigslist for $500 I believe that needs a top end. I'd pop on that before one of those shake your teeth loose yard carts. Here is the link to it and there may be a pretty sauced up motor available for it as well. In any case I'd offer $350 and go from there. You can get a top end for a little over $100.
http://modesto.craigslist.org/mcy/1928066908.html