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I know how big my RES could possibly get, I just don't have the money right now to get a bigger tank. If it was up to me I'd have an outdoor pond type of setup, but thats too expensive. He doesn't need a new tank just yet, but I don't plan on giving him up any time soon (I love my Fat Bastard), so it'll have to happen eventually. Does anyone know of anywhere I could get a tank for cheap? I can get the other stuff without a problem. The 10 gal. tank he's in now has everything he needs, I just need a larger tank. I've been looking for awhile with no luck and it's frustrating.

You can look into other options, like big rubbermaid storage containers while he's smaller and stock tanks when he's bigger. The stock tanks are large (usually black) rubber containers meant for holding food and water for farm animals. They come in a few different sizes, and they're much cheaper than a similarly sized tank.

Glasscages.com is excellent if they have a location near you. Otherwise the shipping is horrible. Craigslist is amazing as well.

Right now is spring cleaning time, so you can look in your local paper, garage sales, and Craigslist for a cheap tank! It's a good time to look for a 55-125 gallon tank. And remember, a 10 gallon tank, the equipment will NEED to be upgraded as well. You'll need a better filter, a more powerful heater, and possible more lighting and other accessories. Also a good time to start looking for sales, esp on canister filters. It sounds painful, you'll probably spend $400-$600 right away, but then your turtle is set for life, practically! Just start looking for sales now and you can space the cost out. I can't imagine a 10 gallon tank working for a turtle minus a hatchling, and they don't stay small for very long ...

Craigslist is a sure bet.

Go with Craiglist!!! I got a 130 gal tank with stand and the filter to go with it for 200 last spring. Just keep your eye out, especially for things like moving sales.

Yup, craigslist is awesome, I've gotten a number of tanks on there. Some people on here have found tanks for less than a dollar a gallon. I've spent anywhere from 55-100 for 30-45 gallon tanks with stands. Also, ask around, as you'd be surprised how many people have a fishtank sitting in their basement and would be just as happy to get rid of it. I've gotten a 55 gallon, a 30, a 20 and two 10s just because people didn't want them anymore.

My friend just got a 40 gallon glass tank off of freecycle. It is a great site of people that just want to recycle stuff so it doesn't end up in a land fill.
I posted my "Want ad" on there but no luck for me yet.
Check if there is a freecycle in your neck of the woods, it is a yahoo group base.