Lots of options:

Trek 800 for $120 http://easttexas.craigslist.org/bik/1392658129.html
And another for $150 http://easttexas.craigslist.org/bik/1383847670.html
Trek 950 single track for $120 http://easttexas.craigslist.org/bik/1379519527.html
Specialized Rockhopper for $75 http://shreveport.craigslist.org/bik/1355089838.html

And last but not least, if I want to drive 3 hours for pickup, there's a company in Dallas selling a Giant Yukon and a Farrago 4 together for $180.

With my limited knowledge, the 950 looks nice, but the seller says it's for 5'5" and under. I'm about 5'7" 125lb. Probably a good bike for my wife, but as little as she rides, her "mart" bike is more than sufficient. Perhaps a different stem and/or other components would fit it for me?

One other concern is that I don't have room to keep a bike indoors. I've been keeping ours under a tarp off of the ground, but some of the components are still showing rust, so I worry about the steel frames.

Thoughts?