If I was to do one, and throw myself in it from 20 ft, I would just go check a place with one, and ask questions, rather than ask a bunch of kids on a website. just my 2 cents
The blocks are expensive. you can get them off ebay sometimes and buy them by the block. I saw them for 1$ each once, but to have enough would be a few grand. Just cut up old couch cushions, etc.
if you do do it (lol do-do), dont worrry about cost cuz you can just charge admission to use it. you know that kids would line up to use it and pay substantial cheddar