I am no pro on rats but I know that I use 16% protein hog feed and chicken scratch for my ASFs. Costs me about 35$ for both bags about 45kg per bag. Both bags last me about 8 months for the 5 colonies I have. With mice you do not want to feed more then 13% protein and I know my farm store here sells 13% hog feed as well mixed with bird seed.

I am not an expert on mice and have no clue about rats at all. But 13% hog feed and chicken scratch/bird seed will be fine for mice.