Here's what I do regularly:

I go to Big Cheese Rodents in Ft Worth, buy 275 live medium adult mice. They run me $0.45 apiece. The Petco around me sells them for $2 apiece, so no thanks. Even with gas the way it is, I come out WAY ahead.

OR

Get a cement mixing tub and make a lid for it, or get a big tank(20 long or bigger). Get 8-10 young female mice(small adult) and 2-3 young adult males. Leave them COMPLETELY alone other than food and water, and changing the cage once a week. Putting them in a closet or in a bedroom where they get minimal disturbance will ensure that they won't get stressed.

After a month or so, you should have babies. Do not touch, bother or otherwise mess with the cage or nest for a good week after the babies are born. When you clean, grab the whole nest and babies, with gloves on if you can, and transfer them to a holding tub or bucket. Put the adults in another container so they aren't trying to grab babies and moving them. Clean the cage quickly and put everyone back as soon as possible.

Food-wise, they need a higher protein diet. Mine get Mazuri 9F(16% protein and 9% fat), plus some dog food, black oil sunflower seeds and old-fashioned(slow cooking) oatmeal. They get cheerios every now and then too.

The main thing with mice is to LEAVE THEM ALONE. They will do their thing and you'll have litters of mice coming out your ears soon. If you notice a female dragging babies around more than she should, or stealing, or eating babies(attacking them, and only eating their heads or whatever, not cleaning up a baby that has died naturally), immediately cull her.

If you have any questions, let me know