I feed my mice small world mouse and rat food, purchased at walmart for around $3.50 per 3 pound bag of food. It gets expensive, especially when you have a lot of mice to feed, and 3 pound bags are the only size you can buy. I have a friend who feeds her mice gerbil or hamster food to save money, as you get more for the same price, but to me, it always seems like it is lacking something, or it would say it is for mice too. Just curious to know what everyone else feeds their mice that might be a little cheaper, and come in bigger (than 3 pound) bags?