Not so sure about the $20 cost. The author is using either 3/4 or 1 inch plywood for the build. And not the cheap stuff. In NY this can run you around $30 and up easy. But still a nice build. The other downside, is the author charges for the plans (5-2.50) for the build, so if you are doing this on your own, you need to figure out the cuts yourself.