If you get the Xylotex, all you need is the motors and power supply. A lot of guys with the Xylotex get motors from Ebay, from a seller named deepgroove1. Very reasonably priced. And for a power supply, a lot of Xylotex users use this:
http://www.mpja.com/productview.asp?product=12424+PS . But, you can probably find a cheaper one on Ebay if you're not in a hurry. search for 24V power supply. Get one at least 5-6 amps.
From what I've read, typically you'll get better performance with the Xylotex than the FET. But thats just what I've read, as I've never used one.