wrk101 would be correct a couple of years ago, but his perceptions are wrong today. The vintage MTB market spiked big time over the past couple of years. However, only the higher end stuff has any real value. Serious MTB riders are quite interested in older rigid bikes.
Trek speced it's MTBs pretty low (e.g. the 950 was one of their higher models, but Mountain LX is nothing special), but yours does a really nice frame and is in fantastic shape. I'd say it would go for just south of $200 to the right local buyer.