Replying to Looking to buy foam? Any advice?

Not sure if this is supposed to be in WTB.

Here's the deal. A fellow newschooler and i are looking to buy some sort of foam pad to protect us when we hit the ground. It will be used to cushion things like wall flips, slacklining tricks, etc. We have looked at numerous bouldering crash pads and they are just a little pricey. Same with gymnastics pads. I was wondering where I could find cheap open-cell foam. Maybe multiple thinner sheets or just one thick 6+ inch sheet. What type of stores should i look into, or any cheap online retailers?

+k for any help

-k for hate/calling us pussies for not just trying it.