rednut - how many rats are wanting to run in the setup? Depending on many you want to run and how plan on running your colony will affect what size tub and how many tubs you need......racks are not that hard to make by yourself - i was absolutely useless at manual arts at school and i manage to build quite a few myself. I use a small nail gun (about $80), pva glue (very cheap), 42x19 pine for most of the framing, plywood strips for the tub runners and aviary mesh which if you shop around is a lot cheaper than what you see in bunnings. I guess the only thing I have which is a bit expensive to build them is a small air compressor which was left over from our old family business. What you will need to spend on tools to do it yourself might be worth it as if you pay someone to build them and they value their labour at a reasonable amount it will probably work out cheaper for you.
Shoot me a pm if you want as I have built a few of these over the years and can give you some pointers.
Cheers,
Dave
these are the racks I pmed you about - one holds the 20l tubs and the other is the 41l tubs.