I just don't feel like spending an hour adding up prices at an online bike shop so I can come back here and give you an answer that won't be the same as what you end up with. If you want the answer do the work yourself...not only will you appreciate all the options available, but your answer will actually be helpful to you since it will contain parts you actually want.

Try Speedgoat: http://www.speedgoat.com/

They have a build kit on special that is $717 - you'll need wheels and tires on top of that.

If you want something more specific start adding up the costs of parts at Speedgoat one by one.