I've managed to pick up a whole bunch of stuff, and will likely begin making the board this weekend.
2 boards (2ft x 4ft x 5/8" particle board) @ $7
3 "furring strips", 8ft long, 2"x1" @ $2.40
Wood screws (already have)
Particle board was chosen mainly for cost. I was initially looking at MDF, but the 1/4" thick sheets didn't seem like they'd stay in place well enough once on the table. The 1/2" sheets were over $8 each, and the first one I picked up had been smashed on one side. This didn't fill me with confidence as to the durability I want for storage. I really liked some sanded plywood, but each board cost $11. So, I went with particle board that is thick enough to not warp and cheap enough to not break the bank. The furring strips were purchased so that I can create a lip on the edge of the board so that dice don't roll off, and to protect against the rather sharp edges of the particle board. This should also reduce splinters.
I also bought a 50" x 100" Woodland Scenics grass mat from Hobby Lobby and a jar of vinyl adhesive that was on clearance. Total price: about $22 with tax.
Pictures will be posted as I begin construction.