If you look carefully enough, you'll find a Truggy for 100 bucks sometime. (Used of course, but it doesn't mean it's bad)
Then you could buy like Linc said a MMM 2200kv combo, and run on your 5S/buy Zippy's

Or you could do this:
Buy a new truggy, sell the nitro stuff. Buy a supersimple ESC from hobbycity + some cheap motor + your 5S LiPo or some cheap Zippys.

Or:
Used truggy (100$), Supersimple 100A ESC (30$), Cheap brushless motor (50$), your own radio, own 5S LiPo.

As you see the last one is the cheapest