are there any foams that i can buy at a store or order to be delivered at a store that arnt insanely expensive i live a half hour north of chicago.
There's got to be a fiberglass and foam supplier someplace in Chicago. West Marine sells fiberglass and epoxy (although it ain't cheap there, see if you can get a "Port Supply" account or find someone who already has one). PVC foam, glass and epoxy is the way to go. You can use an old compressor from a refrigerator as a vacuum pump, or buy a vacuum pump used (I got one from an auto airconditioning repair shop for $30). It doesn't cost that much more to build a board from the right materials. Just takes a bit more time and more skill.
Can't beat ply for super cheap / super easy though. Years ago there was a site that showed how a guy built a light board using 1/8" ply door skins (top and bottom) and 1" styro foam insulation core. He glued the skins to the foam then wrapped the rail with fiberglass tape. My guess is he got -maybe- one season from that board, but it looked cheap and easy to do.