I just bought a used complete 55 gallon setup (tank, hood, stand, filter, etc.) for $100 at a yard sale. Sometimes they don't have them outside and you have to ask if they have any for sale. Yard sales have good bargains. Be very careful and look for cracks. I made that mistake with a 29 gallon that my hubby bought me a while back and it's about to be turned into a hamster or hermit crab cage for the kids. It has a very small crack but it looks like just a few inches of water will make it spread so I'm not taking chances with it.
Good luck finding what you're looking for, but be patient and wait for the right one.