At almost any local lumberyard you will find a plywood sold under the generic name "luan" for a stuningly moderate price (15.00$ canadian for a 1/4" sheet here in eastern Québec). It has only three ply, the outside faces being thin rotary cut philippine mahogany veneer glued on a thicker and lighter core, so its mechanical properties are at best mediocre. However one of its face is wihtout flaw, it is much lighter than a marine plywood of the same thickness and it will bend into fair curves. For building say, a hard chine kayak hull, I would suggest that such a plywood is perfectly appropriate if the hull is to be laminated with epoxy and fiberglass, that is most of the time. But I would like to be convinced otherwise.