Depends on when you want it, and how much you want to spend.
I got lucky and picked mine up from Craigslist, but finding a decently priced one is hit and miss. Also keep in mind that most kegerators are going to be fitted with the nuts to fit a sanke keg (so you may have to cut them off and attach ball/pin lock fittings depending on your kegs)
If you want it yesterday - Ebay is your friend, and I believe there are a couple of vendors who can customize it for you (but this might be a bit more moolah)
-Me