Petsmart has 2 gallon plastic "drum" bowls things for $3 that I saw and thought, "I could keep a betta in there!"

also I like the round SmallWorld Round Tanks things from Penn Plax (medium or large, not the one it says bettas should go in, that's like 1/2 gallon). I think Petsamrt does not carry them but Petco does. Or you could call local places and ask them if they carry them. They are round and that is so cool, I just thought the betta would be really happy in a round tank.