agree on having to go used. Just know that you're probably going to have to spend some money on maintenance early on. I find that a lot of times that bikes are sale because the maintenance was getting high enough to justify buying a new bike. that's not always the case, but I think its the case more often than not.
My suggestion would be to get a Transition Bottle Rocket. Build it big for a mini-DH or FR rig. Build it light for a burly AM bike. I went from a 2009 Specialized Enduro to a BR and love love love it. It jumps way better and surprisingly pedals better. I haven't had it on a rowdy DH track yet. I took the BR on a trail that has a random root sections. On the Enduro, I would just plow through it, but on the BR I would jump most of it. Its not a lightweight bike. Mine with coil rear suspension, 180mm coil totem, dropper post, all mountain rims with DH tires is 40lbs (vs my 34lb enduro). but it certainly hides the weight pretty well.