I saw plans for one where you make the surface the size you want, using pegboard, braced from underneath to make it firm. Build a box to mount the top on, with a hole cut in the side that you can stick a shop vac hose in. Fire up the vacuum, it will pull air down through the holes in the pegboard, taking the sanding dust with it. You can make one 2'x2' and a foot deep for about $20 or so.