not quite anywhere near 400 but i got this yeti asr sl, perfect condition for 1800, yeti and moots make some fucking sick bikes straight from the Rockies. i own a moots road bike, and used to own a hard tail and they had to be some of my favorite bikes. (picture is not exactly the one)
i would save up and buy a dirt jumper, i got a specialized p2 frame and nice parts and put together an awesome bike for about 1k. if you know nothing about working on a bike then i would not recommend building one, the cheapest good bikes that are worth your money would be kona, specialised, and NS bikes.... yes NS makes bikes http://www.ns-bikes.com/
ns is higly recomended they make awsome bikes.