Mountain bikes come in a few price categories that equate to performance and capabilities:
$400 -500 = not for frequent or semi serious offroading
$500- 800 = starting to get capabilities, heavy, slower handling, avoid full suspension at this price
$800- 1500 = valid off road machines, weight is dropping, upgraded components, full suspension will be 30+ lbs
$1500 – 2500 = Solid upper line brand trail bikes
$2500- ? = Light weight, solid components, state of the art performance
If you are into a project, buy a Chinese carbon frame and build one.