I've previously owned two fixed gear road bikes and I know how like to actually ride. I'm 6'0 tall. I found one on amazon "Vilano Blackjack 29er 2.0" for the price of $400. I'll mainly be doing trail rides but would also like to try downhill riding. Need something cost effective. Budget kinda stops at $400.
Budget bikes have crappy front suspension shocks, if you're going to do serious and fast downhill riding...DON'T! Those shocks aren't up for the task and will break, also due to the expense of the shock fork you'll get cheaper components and or frame. You will be much better off going with a rigid frame and fork mountain bike something like this: http://www.bikesdirect.com/products/windsor/flat-bar-hybrid-road-bikes/rapide-hybrid-flatbar-road.h