Here is the inexpensive way I made my design wall.
Home Depot sells foam insulation sheets in the drywall section. It costs about $10 and is 4 x 8 feet. You can easily cut it down with a utility knife. There is a shiny aluminum foil looking side to this foam sheet.
Home Depot also sells spray adhesive (in the paint department) and you can get white flannel very inexpensively at Walmart, etc. I bought 3 yards and covered the board with two sections of it. Spray a little adhesive and start applying the flannel like wallpaper, smoothing it on to keep out air bubbles.
This is extremely light weight, so you can move it, and because it is foam, it is really easy to pin the blocks to if you need to. This came in handy when I had sewed my blocks into columns and they kept sliding off from the weight of the column.
Total cost of the design wall, $25 with tax. And it should last forever!