www.thebookyard.com
I had the same idea. You can buy cases in various states of repair from the link above. 2018 grey is still expensive, so if you don't mind mixing colours it will be cheaper.
I don't have the dollar right now but I was thinking about the Sonnet Breakaway Puck.
Possibly cutting a hole in one case and fitting 2 together like a sandwich, to provide the needed height.