Petco is really out of the way here, but mice are 2.59, small rats are the same, medium rats are like 6$ and large ones are like 10. I order everything frozen in bulk now, and I save a lot more than I would even getting frozen at the pet store.

There are 2 pet stores closer, one refuses to give me rodents since they claim it's cruel to feed them to snakes, the other doesn't even carry frozen or live. *sigh* And it takes about 2 hours each way via public trans to get to Petco.

But still, look around, you will get higher quality animals off of a local breeder and at better prices. You could probably swap your whole colony out for under $20.