My design wall is made from a 4 x 8 sheet of styrofoam insulation that came from Home Depot - it cost about $10. One end is covered with white fleece - the other with black fleece - I use black to audition pastel colors - white seems to suck the color right out of pastel fabrics.
I have a long wall in my sewing room, but if I needed to I could cut this sheet in half and have 2 small design walls.
The fabric sticks to the fleece without needing to pin. If I do pin - pins slide in & out of the styrofoam with ease.
So - - no need to purchase a design wall - just look around the local hardware store and your creative mind with figure out the best materials to use to fit your needs. :)