The best thing you'll find for doing tricks on a fixed gear bike is to go with a Volume Cutter frame, and some strong ass wheels. Everything else is just finding the parts that fit for what you want to do.

there's also the Bruiser by Milwaukee bikes which was designed with tricks in mind. You should be able to build something at the upper end of your budget based on either of these frames

http://www.tricktrack.org/forums/viewtopic.php?t=973