I've gotten two used tanks, one free, one I got on Ebay.
My hospital tank I got during an emergency when I just didnt have a dime to spare and a sick fish. The tank was filthy, but hey, filth cleans and the tank was free.
On Ebay, I found a 65 gallon hex, with a new, "unused" Eheim 2217, ornaments blah blah blah, for $112.00
Best $112 I ever spent. I tossed the ornaments and gravel and cleaned the tank (and dont let anyone ever tell you cleaning a 65 gallon hex is easy when you're only 5 foot 2 inches tall....