Cooler Master has torn through the funding target of its new Raspberry Pi case, the Pi Case 40. Apparently offering better cooling performance than "any other passively cooled Pi case on the market", the Pi Case 40 retails for just €23 (~US$27).
https://www.notebookcheck.net/Raspberry-Pi-Cooler-Master-promises-unbeatable-cooling-performance-from-its-new-passively-cooled-case-for-the-popular-single-board-computer.481467.0.html