I've had experience with used tanks.. it's hard to find BIG ones with little wear on the them. It's easy to find small ones (55 and less) with little wear on them (scratches) due to people moving and not wanting to take them, or just generally thought they wanted fish but found out they didn't.
Go to your local pet store, look there, and hope find any used ones that are still in nice shape. If you can't, shop around your local big chain pet stores, and find the best deal. I do know my local PetSmart sells a 125, but it's like $600+ tank/lights/glass hood.