Relatively cheap too...$14 for a 4' x 8' sheet of R10 foam board, $30 for a foam cutter at Hobby Lobby (which is less of a pain than building a custom unit), $9 for paint and maybe some flock.
The key to impressing the hexes has been using a block of Heroscape singles and then firmly pressing them into the foam. Cutting after impressing the hexes has worked OK. Impressing after cutting may work better and with the remaining material (quite a bit) is what my next line of experiments will be.