In the automotive section at Walmart they carry heavy weight fiberglass. It looks just like the stuff we use to make/repair cowls. It is a pretty good size pack for around $3.00. It is alongside the bondo, glazing putty etc.
In the crafts section they carry basswood blocks, dowel rods, hardwood rails. Another interesting find is the foam rubber used for chair cushions. It comes in packs of 4 (16"x16"x1"thick) for just a few bucks.
Thought I'd pass this along.

WCB