A few ex-military Humvees have fallen into private hands, but don't expect to find one for "cheap". Here are a couple of outfits which deal in them:

Real4WD.com
Xhumvee.com

There's really no such thing as a cheap fixer-upper civilian Hummer. At least, if you did find a wrecked or salvaged one, it would cost at least as much to make it roadworthy as a good, solid used one would cost.