Ok, after talking with my dad (tool and die maker), he managed to find a place that offers bulk discounting pricing for 4" boxes at 2" height for 93 cents each. I can add in spacers to beef out the grid further.

Why are using electrical steel boxes a good idea? Cause is it 1/8" of steel. In a grid, it boosts the strength even further. Combine that with the 3/8" polycarbonate I'm going to purchase that will distrubte the load further.

I'm going to do some price pointing on the wood shortly.