With 1001pallet.com's advice, I learned how and where to ask for pallets that could be repurposed, and found a very helpful locally owned hardware store.
My initial reaction was, "Oh, these are too heavy to be carried on and off stage." But the beautiful surface pieces (minus the structural 2x4's) were perfect. 3x1? 3x1/2? Whatever.
I took two pallets apart and built a 3 foot by 2-foot pallet wood sign with a "kickstand" on the back so it could stand alone. Then I sanded it so it could better take the lettering, and white-washed it with watered down white paint to make it look more like driftwood.
FYI, the final lettering is darker in this picture, thanks to sharpies. Actually, cheap dollar store sharpies which splay out, but are still more controllable than paint and brush.