This one on the other hand WAS the cheapest! Inelegant, but it does the trick, at least for a few trips. Not sure how long it will stand up though. Simple piece of cardboard from an old binder, a couple pieces of elastic, and a stapler. It would probably be better to sew them down, but I have no idea how to sew. I have a Sewing Machine, I just dont know how to use it.

I ended up double taping a piece of felt to the back. The staples didn't protrude enough when going through the elastic and the board and so were a bit pointy and snagged. That solved that problem.

Could have made the elastics a bit longer, too.