I just purchased a 4'x8' sheet of that pink colored, sealed foam insulation board from Home Depot, covered it with fleece or flannel. It's light weight, you can attach it the wall, mine is not. My blocks stick to it very well, without pins. I can layout my blocks as I finish them to decide what order I want the in before stitching them together. I can "stick" the entire top up there and it sticks very well.
Our guild has about 4 of these and when we gather sometimes for a day of stitching or a class somewhere, like a church or gym or the senior citizen center, we have boards that are light weight and portable.
Probably cost me about $30.00 with the board and the fleece. I attached the fleece with my "handy-dandy" stapler with 1/4 staples, then took clear packing tape and went all around the edges of the fabric to cover the staples.
Good luck.