I just started "again" last weekend. I used to do all kinds of crap offroad. I wouldn't spend $800 on a bike unless you really serious. $400 would get you a good enuff bike to learn on and abuse and if you decided to be hardcore then you can get something nicer later.
If your going offroad, it might be a good idea to get a hardtail style bike rather than just a stiff bike. But if you stay on concrete trails or smooth dirt than a stiff bike will work great and its cheaper too.
