I've seen pepperocini jars at wholesale stores for around $4, they are just shy of a gallon. The only problem I see with them, is they're a gallon tall, not squat. I keep oogling the pickle isle of all the local grocery stores, hoping some good deal will wander through.
More obvious places would be second hand stores, such as the Salvation Army, and St Vincent DuPaul's -- the only big problem with these places, is the stock wanders in whenever it chooses. Generally they get a big influx of bowls about 2 weeks after the 4th of July, when all the game-won goldfish pass on. You can find some great things there, I found a totally sweet folding Japanese bicycle there, once, for communting, only $20, but I had to beat other people off with a stick to walk out of the store with it. It's all in the hunt.
Jars made for vacuum sealing (such as Food Saver) are expensive, but if you've no options, they're a very clear, sanitary selection. They don't suffer from the fogginess that tupperware suffers from, and all their sizes are shelf advertized.
Many times, vases (gasp), are a gallon in size. Whenver you see a picture of a frog or a fish on the vase... it's probably half a gallon, the company that markets to betta-vase people generally only sell 1/2 gallon size vases, select something roughly twice as big. At least, that's what I've observed, locally. In fact, I found a 2 gallon vase at the Salvation Army once, for a friend -- huge, heavy thing. She's kept a betta and two ghost shrimp in there for something like three months, now.
And the, of course, there's the internet. Find a shop that sells more than just aquariums/bowls, and order the bowl along with lots of other stuff you need -- like fish food, cat toys, water treatment, etc -- that way, you'll save money on bulk where you lose in shipping.
/secure.foxinet.net/ccw/orderform.html
