Ironhorse makes a good bike with SGS sport for 1100$ american with a 5 year warranty that will suport freeriding and is very upgradeable. For 500$ more you can get the expert (I think) which is a huge upgrade. Right now I don't think there is a company on the market producing as good a bike as cheap.
Specialized is another one that produces good bikes cheap and you should be able to find something in that range that is upgradeable.
(bighit expert maybe)