You can get a trailer hitch tire carrier for $100, but it wont have the fold down option..

I like your idea for $200-$250. But would like to see two preload bolts to reduce sway/rattle. One to put pressure on the vertical bar; it would push the bar outwards and jam it via the release pin. The other would have to be on another tab underneath the horizontal section that goes into the hitch; this one would put pressure on the bottom of the hitch, effectively pulling the whole thing "down" and would reduce rocking and sway.