The guy at Bayonet in Dallas told me that the reason ammo cans are so expensive, if you can find them, is because many years ago, the govt started crushing them and recycling them as opposed to letting them go to surplus for sale. Don't know how true that is, but it sounds about right...
If you want great cans at a fantastic price, skip the stores and hit up gadawgfdan706. I've bought from him before and he treats you right.
http://www.theoutdoorstrader.com/threads/577273-FS-ammo-cans