I currently have my 3 ball pythons and dumeril's boa on rats. Green Tree Python will only need to eat adult mice, so she doesn't count in.
How many snakes do you think you could have for it to start becoming really economical to breed your own rats? Six? Ten?
What's the total cost of caring for say 2 females and 1 male rat per month, plus raising the babies until they become "small rats" size to euthanize for feeding?