Try the 400 gallon stock tank from toter.com If you live in the southern half of the US and are close to sea level you could probably keep adults in the stock tank outside and only use a heater to keep an ice layer from forming on the coldest nights. Find a fish hatchery/ farm to get fingerling bass, catfish, etc. for cheap (like 100 fish for $15 or so). I buy frozen whole baby chickens from a reptile store and crawfish (in season) from seafood stores. I also get shiners from a local bait shop & Oscars from pet stores. Other people buy rats.
Kevin