Critter keepers don't have a specific gallon measurement on them, but I know I paid for a small one at around $7 to quarantine a baby goldfish. It held significantly less water than my 2.5 gallon and I didn't trust it enough to be filled with water, only a third of the way, while holding the handle because it felt unstable. It ended up cracking very easily after I got home, which is after the goldfish died and it wasn't filled with anything aside food containers.
Honestly, if you have a better you're going to have to have at least 2-2.5 gallons anyway and the equivalent critter keeper is probably going to be more expensive or just around the price of a good tank, which makes it less of a bargain. I used a hexagon shaped 2.5g tank while in college and had a spare tank for my guy when I came home during breaks. He travelled in his PetSmart cup and seemed happy.
This 2.65 gallon tank is only $20 online, which is not bad for a tank. http://www.petsmart.com/product/inde...ductId=2753107
It also includes gravel, a filter, silk plant, and I believe a light.
From that same brand, in different colors and gallons, there are other tanks more affordable if that one won't do with your budget.
The pink 1.77 for $15: http://www.petsmart.com/product/inde...ductId=3981820
There used to be a blue one for sale at $5 but I cannot find it anymore.