I made my design wall for less than $15. I bought two large foam boards at Hobby Lobby, a can of spray adhesive (Hobby Lobby again), sprayed the foam boards with the adhesive and covered them with batting from my stash (I wanted it to be kind of "puffy" so that a pin would stick in it), then I covered them with flannel purchased at (you guessed it) Hobby Lobby. I mounted the boards separately with "L" brackets (Wal-Mart, they were not expensive) and just to make sure the flannel stayed on I attached small black paper binder clips (Wal-Mart again, not expensive. I went to Hobby Lobby 3 or 4 times that week, with my 40% off coupons, but it was on my way home. I really, really, really like my design wall. :-)
My son bought the sewing machine and cabinet for me. He knows I like "old stuff" and someday I'd like to have it restored.