Yep, used 10 gallon tanks are the bomb. They're already stupid cheap to buy new, and you should be able to buy used (don't hold water, cracked but not broken) tanks and lids very cheap at garage sales, on classifieds such as Craigslist, etc.
Racks are awesome, too. Never had one of my own, but worked at a pet store that bred mice and rats in rodent racks. A breeze to maintain. Food on a portion of the wire kept it out of the bedding. Tubs are super easy to clean--dump, wipe, add new bedding. No nasty crevices or tank lips holding in the last dredges of bedding/poop. If you have a watering system? Top it off when needed, and otherwise the only big worry is a valve getting stuck in the "open" position and flooding a tub (had that happen a couple times--ewww!). Plus, the space thing--when I first started working there, there was still some 15 or so mouse colonies in 10 gallons. By the time I left, they'd moved the last of the colonies into racks, and what took up one big wall suddenly was condensed into 1/4 the space.
Tanks are fine with only a few colonies to deal with (which is what I'm dealing with right now--only just now started up with the mouse breeding thing again), but racks are definitely the way to go if you're looking at having several colonies running.