In most cases id say its not worth it but in your case it really sounds like it would be imo. Plus you could always cull and freeze extra rats, or sell nice ones as pets! Ive heard some people on here say that their snakes tend to eat better on live. (Not trying to start an argument by saying thats true, ive just heard some people say it.) When i have the space and time to, i would love to breed my own rats.
EDIT: how do you have space for a rat rack but not for a freezer? They make smaller chest freezers you know