If you do buy a clone, be sure to do a THOROUGH tear down and inspection. I've seen too many dry diffs and cracked diff cups. Also be aware that the plastic can be a bit more brittle (RPM is your friend). Also make sure that you have a good kill switch like the Killer Bee.
You can look for used HPI Bajas on our sister forum. I bought mine from @Nitrobuzzard and haven't looked back.
EDIT: Forgot the link: http://www.largescaleforums.com/