I will keep saying it until it sinks in or I get the carpal tunnel from typing...
Doggy Bag dog food from Tractor Supply Co.
That is ALL I feed my rats. They are free fed in a rack system and they are all doing great. There is no reason to spend a lot of money feeding rats fancy food. These animals evolved to live, breed, and thrive in less than ideal conditions with less than ideal food to eat. If you are feeding anything else you are wasting money in my opinion.
I get it for about $0.27 per pound.
If you only have a handful of rats you can feed them whatever you like. When you are going through a few hundred pounds of food every week you need to explore every possible option to make things more economical.