I have a need for about 16-20 large boxes, measuring 50" long, 18" wide and 16" deep, and with a hinged lid like a casket, or removable entirely. However, they need to be rigid and as lightweight as possible. I was considering making them out of 1/2" plywood, but I am not confident that the box will hold together well without a bunch of heavy straps or braces. Does anyone have suggestions on how to do this? The contents of each box will weigh between 60 and 100 lb, so they will need to have some kind of handle on each end for two people to carry them. I also need to be able to stack the boxes four high if possible. Almost like old war-era wooden ordnance boxes. Final requirement is that they need to be made for less than $20 each.