SHeet metal (aluminum) project boxes of about that size can be bought from an electronics distributor for about 5 dollars.. Try Mouser.com, they don't have a minimum dollar amount. I'll see what I can find for you, I've got a Mouser paper catalog..

Try these part numbers at Mouser, there is a catalog page link if you want pics, etc. Don't include the part in parentheses.
These are all between $4 and $12..
563-CU-3005A (Bud)
546-1411-L (Hammond)
537-TF-779 (LMB)
537-J-879 (LMB)
537-UC-971 (LMB)