What mountain bikes are good for very rugged terrain? Looking to keep it under $400 if possible.?

With bikes, you often get what you pay for. Unfortunately, $400 is a pretty low price point--better beginning mountain bikes start in the $600 range, I'd say. With that said, however, there are still some options available for less than or close to $400. Try the KHS Alite 300 ($379), the Trek 3900 ($479) or the Raleigh Mojave 5.0 ($500).