for some reason all the stuntbikes on my craigslist are always $3k or more, it's ridiculous. That F4 would work, but you can get a clean F4 for $2k. One that's already beat to hell shouldn't cost $1800 still. This time of year you can find half decent bikes all over craigslist for $2500. Lately I've seen a 600rr, an R1, and a couple gsxrs all for about $2500. Keep your eyes open and you can definitely find something cheap.
I'm also hoping to pick up a bike to mess around on next fall. Not a dedicated stunt bike, just an all around bike to fill in the things I'd like to spare my buell from, goofing around included, but also random things like questionable weather, boring highway miles, leaving it parked on city streets, stuff like that. I think I'm gonna try to find something for no more than $3k, but hopefully closer to $2k, strip it down from the fairings and put dirt bars on it, and just ride it without a second though of where I'm going to find replacement parts for it in 5 years. Hoping for a gsxr750 or maybe a 636.