Personally, I would stick with the old Trek Mountain Track. Those old steel bikes were better than a lot of bikes these days, and for the type of riding you say you do, I don't see any reason to have to buy a new bike. Sure, things are going to need to be replaced after 9 years, but the frame is still most likely pretty solid. For $195 you can buy a new lx derailleur (~$40), new avid v-brakes (~$25), new barends (~$15), new cables (~$15), new cassette and chain if needed (~$50), and a professional tune-up (~$50).

If you did that, your bike would thank you, and you would have a much better ride than if you spent that same money on a $195 Mongoose.

Then again, there's always that thrill of getting a new bike. If you found a decent used bike for $200, that would be a good idea as well.