I used the 5 gallon kritter keepers for the first few months, then moved them into their 20g long tanks. the kritter keepers are only 5 bucks, and pretty escape proof. Also saves you a bit so you can get nicer big cages later;)
:Baby corn snakes can be kept in 10 gallon or even 5 gallon tanks. They will eat each other, even if it is rare. I keep mine in different cages. I recommend buying a 5 gallon cage and moving them to a larger cage like the Vision 211 when they are 6 months or so old.