Where can l buy a mass quantity of foam and how much does it cost?Does it come by the square foot?

Go to the nearest gymnastics school. They can tell you where to buy it. You might even be able to buy their used stuff cheaper. l do not know how often they replace it, but when my kids did gymnastics they changed out the foam in the pit and just gave it all away.

A cheap way.look for old couches, beds, etc. Me and some buddies filled a 30x30 pit with all that. Works fine, we just had to make it a little deeper just to be safe.

Or check out the link.

well do an internet/ google search if you already havent or yeah gynastics school, couches pillows your are pretty much there