That's a common rip off like icedgold10 said !! A good way to lose the item and your money !!
Check places like home improvement stores, sears, ect for large boxes !! They get all sizes !! Might let you raid the dumpster or if you know someone that works there,, tell them the dimensions you need !! They can watch as items are unloaded and grab a box for you !! You can cut it down if its a bit oversize !!