2" 4'x8' ( actually 2 of 2 x 8) sheets of 700KPA XPS are 115$us (12 sheet order min)

That's less than 30$ a ½" sheet. Assuming they are hot wired to ½" thick.

A 2" sheet of cheap XPS (that you crush to ½") will cost most all of that. But lets say you have a coupon and get it for 20$ a sheet. Saving 10$ a ½" sheet.

A Ex40 is less than 30 sheets? So, build a heated and cooled 80 Ton press rig for 300$ and break even? Is it not much more likely one will spend way more and get an unknown material that is highly variable?

What are you fighting for? It will take a lot to even get a workable material, if it is even possible, and a lot of testing ($$$) to see the properties it will have, and you will never have the volume needed to approach some sort of sigma of reliability.

Then you want to build an ocean going vessel out of it?