dude, you could get 55s for like 50 bucks on craigslist... i got all of mine from there and they had no problems, got all 3 of my tanks from different people.
they may come to you a little ugly though, but nothing a good scrub or re-sealing wont cure. (unless its calcium but it vanishes with water).
the one thing i would NEVER buy used is a filter though. the motor on multiple occasions i received were cluster****ed and had either broken parts or un-replaced/cleaned parts with old VERY built-up fish crap in them! you could doom your fish the moment you stick those filters in there cause often the old feces and other rotting particles break loose and send your fish up really fast.
