For a finished 2" cutting board approximately 10.5"x16" materials run about $90 ($90 includes glue, mineral oil and carnauba wax). Between the cuts and waste it is not an efficient use of materials. The good news is that for every 2 tumbling-block boards I make I usually have leftovers to make one of the Indian-blanket-design cutting boards. The blanket design is very efficient to make which drops the average cost of a 3 cutting-board run to about $60 per board.
As for the underlay for the Thien sled, I happened to have a thick piece of OSB and a 1" piece of melamine laying around that I stack on top of one another to make the underlay. The dimensions of the sled are approximately 2.5" thick, 12" wide, and 5' long which is perfect for the initially dimensioned rough-sawn boards that I typically work with. Like you I initially borrowed my wife's glue gun, but in the interest of peace have since bought my own

-Erik