Relatively inexpensive. I have rats and won't have mice (again) because of the stink factor, though others will tell you if you clean obsessively the odor isn't a problem. I feed my rats a mix of Ol' Roy dog food (the only dog food that's ok because of its lack of dyes, though the WalMart connection may put you off), uncooked & unsalted peanuts, rodent lab blocks (buy in bulk if you can because chain pet stores mark it waaaay up), fresh fruit and veggies as available (apple cores, for example, since my kids miss a lot of the apple meat when they eat), and occasional other treats (corn, sunflower seeds, etc.). I think we use about 1.5 cups a day of the mixture for 6 rats (1 full-grown, 5 subadult to young adult), plus the other stuff as noted.

The 5 rats are in a cage we got for free, and the other one is in a cage I built for less than $20, and both cages have (free) newspaper substrate, water bottles, and freebie-type hides like tissue boxes. Not counting caging and caging accessories which is going to vary all over the place according to your choices, I think it runs less than $1 a day for all 6 rats.

Edit: I should have mentioned that it's a good idea to have separate cages for males and for weaned juvies by sex, and I do have those available, just no need to have them set up that way until someone is pregnant.