Why don’t you check out one of the knowledgeable review sites out there – this place seems spot on and could be just the place for the sort of advice you need:
Contact us any qwestions about membership, what were about intrestesd in starting mountainbiking on a budget, what to bike to buy
They’ve also got some sage words about AM bikes too:
BEGINNERS GUIDE TO ENDURO/ALLMOUNTAIN
written by tom smith
what to look for in a beginers bike?
a good frame is essential if ever you decide to upgrade your bike
reliable drivetrain your going know were fast without descent gears
fairly short stem 70mm roughley get some control whe shralpin
chain device will help when it get a bit rocky or rooty
wide bars and your a nutter if you dont.
cost: 2500 NEW! cost; 1500-1800 2ND hand