On the breeding racks I use medium size 16"x12"x4" cat litter pans. I purchase them from Dressler's Dog Supplies for $1.55 to $1.75 depending on the quantity purchased.
Item # DOS-22001
www.dresslersdog.com
1-800-622-4669
If you want 12 or more pans at $1.55 each you will need to call and place the order because the website won't factor in the discounted price.
My holding rack pans are Sterilite containers that measure approximately 34"x16"x5˝" on the outside rim. You can find these at WalMart, Target, etc.
NOTE: The Sterilite containers do have edges on the inside that the mice could easily chew on and escape. I have NEVER had a chewing problem maybe because I pull my weanlings at 18-21 days and they usually stay in the holding boxes only to 28 days old before they are sold. They may be too young to be concerned about escaping. Some do stay to 5 weeks and still no problems. This is my experience - others may have terrible stories to tell about the same containers. 
Brian
P.S. Do you have a website for Wade's Weptiles & Wodents?
Dressler's - cat litter pans