If you visit Fort Worth Omaha's is definitely worth the visit. Boxes are cheap if you show up in person and pick them up from the store. AMMO BOXES-Omahas Army/Navy Surplus -
The best find for me has been the Army/Navy Store that is right beside Hot Rod Arms here in Tyler.
I picked up a medium sized can in great condition except for a few rust spots around the handle for 10 bucks. I use it to hold my boxes of 7.62x54r ammo and it works perfectly.
I think the bigger .50 cal cans run about 20 bucks or so but I could be mistaken, it has been a couple of months since I have been there.
So you might want to check local shops like that or any kind of Trade Days where there is a lot of people selling different stuff.