…
Where are you located? If Las Vegas, NV, I have a great store for you. The cans are $5 ea.
I’ve been looking for 50 cal. boxes also. Will this store ship out of state?
Not sure but let me get back to you.
buyer of ammo cans beware 
http://www.calguns.net/calgunforum/showthread.php?t=171995&highlight=ammo+dump
Just spoke to him and he’s not shipping. Sorry.