For that amount, you probably want to start scouring E-Bay for used parts and ask the local shops if anybody has a used rig they want to sell. If you find something that looks promising, you can drop a thread here and ask others what they think.
I agree with the LBS. I am mainly a roadie but I also had a hardtail. It wasnt much, it probably was worth about $450. I went into my LBS and talked with the mechs there to see if they heard of anyone looking to sell or trade a cyclo-x. They did and we hooked up a few days later to see if the trade would be a good fit. I couldnt believe it, I got a perfect sized Redline with ultegra components...one ugly paint job on it, but Im not complaining....its called theft deterant!