Dont think about making extra money think about how to get by by spending less.
Buying rats to feed your snakes frozen or live is expensive.
Breed your own.
Cost of rat food is cheap if bought at feed stores in 50 pound bags.
I spend about 20 bucks per 50 pound bag and that lats a long time.

The most expensive thing i buy is Aspen bedding. I get it at tractor supply company at 10 bucks a bag. I use it for all my pets.
If you want to go cheaper there is Equine Fresh pet bedding. I have never used it myself but i heard its ok for reptiles and rodents.

Also build your own racks. They dont have to be pretty they have to be functional.