At that price point, you should be able to get a 27 speed hard tail with a Shimano Deore Drivetrain and mechanical disc brakes.
Something like this Marin will work nicely:
http://www.rei.com/outlet/product/775003
Here is an Iron Horse:
http://www.performancebike.com/shop/...tegory_ID=3050
At that pricepoint, I would avoid brands like Trek, Cannondale or Specialized. Go for something like a Haro, Iron Horse, Marin, Fuji or other second tier brand. You still may find a leftover 07 bike if you shop around a little.