That is amazing. And I thought my CV 21mm f4 was compact! Cannot see spending $656, not in my budget. However it seems reasonable for a limited production lens.
Now here is what I think would be neat. If the company that makes the little Slim Devil camera, with it's 22mm, 2 element plastic lens would recompute that lens for a flat field (in the Slim Devil the film plane is curved) and mount it in a plastic Leica M body cap as a fixed focus "fun lens" that would sell for no more than $30. If they added a plastic, 2 element shoe mount aux. viewfinder they could ask $40 for the combo.