Wow! You can put your weights/dumbells on that thing!
It wouldn't be too hard to make one of these, it is just a flat piece of wood (use some plywood or mdf) with cuts in the right spot. Try making a template out of cardboard first, and figure out where cuts need to be made, then transfer it to some wood and cut. But for $10 it is a steal, and seems very handy - only if you spend heaps of time in your car when you're not driving, however.