If you do decide to breed rats, definitely, definitely try to find someone local who also breeds rats.
I breed my own, however, if I'm ever short on rats, I have someone I go to. I get smalls and mediums for 75 cents each.
It's nice to have someone you can go to other than a pet shop or reptile shop. I know the rep shops around me charge $2 for a sm....which isn't too bad except for when I have to buy a lot. I prefer to save money when I can.