Well the cost is directly related to the amount of resources used in each size ( paper, dyes, laminate) and the more used the more it costs.
And this one isn't finished so I cannot predict what the final dimensions will be but I will be close and give an estimate. so here goes
As the poster stands right now ( length versus width) it will come in two sizes. If the proportions vary quite a bit - dependant on the number of cars that get added, a third size may be offered.
Anyway as it is right now the two sizes it will come in are
24 x 35.5
and
34 x 50.3
Now it can come in two different formats, heavy bond or laminated. The bond is 38 pound. For a comparison the paper in your printer is 20 pound. Its pretty robust. The second format is laminated.
The prices at these sizes are
24 x 35.5 - bond=$14 - laminated = $18
34 x 50.3 - bond =$18 - laminated = $24
Most are really not prepared for the size that the larger ones are. Yeah its easy to lay it out on the floor with a tape, but when they get the actual thing they are sort of overwhelmed. Anyway - that's where its at as of now.