If simple is the issue . . .

. . . just buy a 4'x4' folding card table. Use some spray contact adhesive to glue a 3'x'3 peice of felt centered on the top. Apply a different color felt to the 6" perimeter.

This require 2 peices of felt (1 - 3'x3' & 1 - 4'x2'), a can of spray adhesive, a pair of scissors and a ruler.

This gives you a fold-up regulation battlefield, as well as a larger area if you decide you want it.