What size do you need? If it has to go in the car, it will need to be foldable or assemble on site. I think it was Sewmanyways.blogspot that had instructions for a plastic pipe frame and a flannel pillowcase style small design board.
I have used a large piece of cardboard with flannel glued on. I had it fold in the middle so it could go in my car and the fold lets it stand in a V shape on a table or floor. I " borrowed" a large piece of cardboard from between the paper towel layers in the Walmart. I did ask first and they were glad to get rid if it. Another possible idea is the cardboard backboard project displays that are sold for student projects here. I don't know if you have them at your office and school supply stores there though?