Here's an easy rat rack setup I found. I built one module/cage so far. It's about 60 dollars with pieces from wal mart for the rack and four containers. Basically, it's just some plastic shelves and modified storage containers.
Details:
4 Rubbermaid Latchable tubs (#3C91), 50 QT clear, 26.1" x 10.4" x 15.6"
1 DuraShelf (#9144), 4-Tier Free Standing Shelf
4 water bottles. and a small amount of hardware cloth/mesh
In order to cut the tubs you need patience and a soldering iron or wood burning kit. Don't try to cut it with a knife as you'll you'll just end up cracking the plastic.
Well i bred rats for a while and i have to say it was way cost effective, they were poppi out so many pups i had to sell them to the pet store cuz i didnt have anymore room in the freezer. Gotta find find the cheap food and cheap housing!