And then there's these: http://www.amazon.com/Petmate-Jumbo-...tty+Litter+Pan http://www.amazon.com/Ace-40-7002-Ut...rds=Mixing+Tub

Might be a much cheaper option for the tubs. Definitely have to make sure the shelf clearance is perfect, and line the bottom of the shelf with something, but you'd end up saving quite a bit in tubs. I haven't checked to see if Ace actually carries them in the store, or if the same thing is available cheaper anywhere else. Home Depot's mixing tubs appear to be about 1/2" too big (usually not a concern, but with the open top I'd be worried that they'd be able to work their way out.) and Lowe's doesn't list any on their site so I'd have to actually go into the store with a measuring tape to see.