Just got back from Homedepot, they don't have any blue foam here.

I saw some 3/4 laminate particle board and some other hardwood, not sure what it's called. I looked at the plywood and it all looked warped in some way.

$30 for the GP board plus shipping; there has to be something else I can pick up locally to build on. If the GP board is only pine I should be able to get a large 48X24 piece from a lumber yard to work.