10 gallons is fine- in fact, you can have your betta in it, and add in 2 more cories to make them all happy :)
You do what you can do for them- even if it's waiting to get the 10 gallon, just as long as you keep doing the water changes it should be fine for a while.
Luckily a 10 gallon isn't all that large, so it wouldn't be too much bigger then the one you have, foot print wise.
I looked on the Walmart site but didn't see the $30 one.. just a 5 gal for $32. Even that would be better if you can get away with a 5 gallon :)
Last edited by Myates; 12-23-2011 at 03:14 PM.