There is a great deal on an 01 NB that is pretty much ready-to-track. I think you could get it for a little over $6k, and it'd cost closer to $8-9k to build it from scratch. They guy who owns it knows his stuff, and John Wags built the AST's for it.
http://www.dfwmiata.com/threads/26872-Fs-2001-nb