You can find a lot of small DC only inverters on ebay and sometimes craigs list for a good price.  If you want an AC/DC machine with high freq you will have to hunt a bit to get a good price.   I always check with state sponsored auctions/surplus, sometimes you can get away with murder at those things, but rarely get to test it out first.   Here is a site or two you might check:

http://www.usedequip.com/ss/2175/0W1003.html
http://www.smfmachinetools.com/tools.htm
http://www.weldplus.com/welderlist.asp
http://www.usa.gov/shopping/supplies/supplies.shtml
http://www.usedequip.com/ss/2175/0W1003.html

Got a lincoln tig250/250 idealarc with ac/dc, hi-frequency, water cooled torch, on bernard skid with old style hand control. Nothing wrong with it just don't need 2 machines. 800 and its yours.