Here's another item that isn't very common on the used market, the Ricoh GR 21mm 3.5 lens. It's the LTM version of the lens from their GR21 point and shoot camera. Ricoh also made a Leica mount version of the 28mm 2.8 lens from the GR1, but I imagine the production on the 21mm version was pretty low. These came with a matching viewfinder and hood, which are included with this one.
It's very cool, and it's rare, but it's also $1,735.00. That's a lot cheaper than a new Elmarit-M, but you could buy 4 Voigtlander Color-Skopars for that price. And the Voigtlander comes with a viewfinder also.