Very cool Ben!
A Miata would be a very cool project car. I just dug up some info on wikipedia
here. It looks like the older you get, the lighter they are.
1989–1997
curb weight - 2070 lbs.
Cd - 0.38
1998–2005
curb weight - 2200 lbs.
Cd - 0.36
2006-Present (for kicks)
curb weight - 2414 lbs.
Cd - ?
The Neon would also be a good conversion. The body does look like its in very descent shape, and it sounds like it'll run enough to not have to tow it home.
1995 Neon
curb weight - 2380 lbs
Cd - 0.33
I browsed through craigslist quickly too searching for 'bad engine' and 'blown engine'. There isn't a ton to choose from.
91 Civic - $700
http://madison.craigslist.org/car/531870401.html
95 Metro - $350
http://madison.craigslist.org/car/523728067.html
94 Tercel - $300
http://madison.craigslist.org/pts/513921781.html
89 Escort - $300
http://appleton.craigslist.org/car/544607393.html
94 Prelude - $800
http://appleton.craigslist.org/car/519658292.html
300ZX - $350
http://milwaukee.craigslist.org/pts/553594879.html