I thought about glass over foam, but I also saw this company
SingCore - Patented Honeycomb Torsion Box Panels | New inventions are making the world a better place.
they are near Olympia, Wa close enough for me to pick up and their 4'x8' 2" thick panels with plywood on each side are $160. I don't know how much more to make them aluminum on one side.