Need help selecting a starter trail bike $250ish for 250lb guy.?

My best friend and I got Wal*Mart Next and Mongoose bikes for $100, but they weren't crap. After going riding on some serious state park trails the derailleurs broke, the breaks are failing, the chains are slipping, and the pedals are popping off. Luckily they have a pretty liberal return policy with the $6 protection plans. I realize that adult males riding aggressively are going to tear up $100 bikes within a couple of rides. I don't care about flash or style, but I need something rugged enough to ride regularly off road without breaking the bank. What do cops ride? Those mountain bikes look pretty stout. I know the government is not buying $800 Treks and Giants. Can I get something decent now for around $250-$350 that will at least last for 2-3 seasons until I am good at mountain biking and can decide what I really want to invest in?