I have 10 snakes and breed my own rats. I also feed rats to my ferrets.
You generally want as many female rats as you do snakes, give or take.
I have pet quality rats and I sell off the really beautiful ones and feed off the rest.
For any kind of top eared rats intended for a pet, I sell them for $5 each. Rex or Dumbos go for $10. But I'm in the process of breeding out the top eared trait.
My American and Russian blue dumbos are in high demand. So just for 5 pups, that's $50. A 50 pound bag of Mazuri 6F is $30 for me and lasts around 2-3 months. 5 babies more than pay for a month's worth of food and bedding.
I really love my rats, so I don't mind cleaning after them. They're fun little critters.
But I'll admit that getting started wasn't easy. You won't break even until after the first couple litters.