Just an idea, but has anyone seen the cardboard folding display boards. Large center section, folding wings. What if that was covered with fleece, even using spray basting, would that make a usable portable design board. I have no idea if this would work, but recall seeing the boards before Christmas at Staples when shipping gifts.
If necessary duct tape or masking tape could be put around the edge to keep whatever fabric is used to cover the cardboard. Wouldn't last forever, but might be inexpensive enough to be doable.