Government Liquidation is good if you are willing to do the auction thing and then pick it up yourself (in most cases).
They also have a spinoff site called:
Uncle Sam's Retail Outlet
You can get M2A1 ammo cans for $7.99 apiece or M19A1 ammo cans for $5.99 apiece.
I bought 6 of the M2A1's last month and with shipping, it was $77 so each ended up being almost $13. Perhaps in bulk, shipping will get the price down a bit.