Sometimes it pays to think outside the box on the whole cage thing. Rats should really be kept in twos for socialization and two active female rats need a lot of space so the cages designed for rats are sometimes too small. the ones that are big enough are often too expensive. Make sure you check the paper, freecycle, ebay, etc. People will sell old cages. A bird cage will work with levels added and the doors wired shut, a large aquarium will work with the purchase of a tank topper, a ferret cage will work with some chicken wire or mesh wrapped around so that the bar spacing isn't too big etc. There are a lot of ways to save money on caging.