ASF are also very prolific breeders. You would have to either feed off the male after he breeds the female, or buy him a male partner to live out his days with. You'd get anywhere from 10-20 rats in one litter. That's 10-20 weeks of food. You'd also have to have at least 2 tanks big enough for the males and females from the litter, and if you've ever sexed a rat before, ASF's can be tough to sex at the weanling age. (4 weeks) If you get it wrong, you'd be over run in a few short weeks with ASF's, and that is expensive and stinky.

For one snake, it's just cheaper and easier to buy either bulk FT or continue to buy live once a week.