HAHAHAHA… OK I am actually thinking about this. The author basically uses a sheet and 1/2 of 1 inch foamboard with an old sheet, Great Stuff/gorrilla glue/tite bond II to hold it together, and outdoor paint. Figure $30 in materials. And it seems to work. No fiberglass, no bending of wood….this looks like my kind of build.
http://www.instructables.com/id/Seafoam-Kayak-the-Unsinkable-Foam-Kayak-Anyone-Can/