I will tell you this. Design looks good, however, cheap is not a good word for what you want to build. Ok, ideas: you will want to buy at least 3/4"(7 ply) cabinet grade plywood either in oak or birch. to finish the edges you will just need iron on edge banding. You will be able to build most if not all of your project using 3/4" plywood. For structural members not seen just use 3/4" A/C pine plywood. OR to another extreme, just use good straight 2x6's, send them through a planer once to get them looking nice, then the jointer to square up the edge, and go from there. you only basicly need to build a couple boxes for support in the middle of the water bed, and 2 sheets of 1/2" plywood to span the frame. A water bed must rest on supports directly to the floor! Each gallon of water in the mattress weighs about 8 lbs. plus the mattress, plus you and your sugnifigant other... so do not try to suspend your water bed mattress If you attach either a 2x4 or 2x2 as a ledge the whole way around the frame, build 2or 3 20"x 20"x (however high) boxes, cut and lay your plywood tight to the frame, you will be good.~Bob