I just made a 6x8 foot design wall with 2 pink insulation boards at 14 dollars each from Home Depot. Cut one in half lengthwise with a box cutter. Then used wide black tape on the seam. I covered it with a flannel sheet I already had. Folded in to the back and used a regular house stapler. It is sitting on top of the baseboard and being held in place with a few push pins.
So mine cost 30 dollars.