There is a BIG difference in a $250 MTB and a $500 MTB if you plan to take it in the dirt. The service fees in the first 6 months on the $250 bike will cover a $500 bike. Buy something decent to start, w/ better(durable) parts that will last the first yr w/o having to change the cassette, chain, rear D, cables. Upgrade the parts as they break. Hard to upgrade POS 7-8spd speed stuff when no one makes them any more. Try to stay in the 9spd country and upgrades for low end to mid grade will be less painful the wallet.
If you stick with it for that first yr, you can prolly sell that $500 bike and upgrade into a $1000-1200 bike where the next performance bang for buck goes. Then it will double again
