Walter -- did you decide yet? Just curious. There are so many good choices out there. Lots of good advice on this thread as well.
Although prices are creeping up, there are still lots of good (used) lenses out there. Reasonable prices can be found with luck and patience.
I have the ZM 50/2, it's a beautiful lens. I also have the Summicron DR 50/2 (no goggles), another timeless lens. Both are very different animals. I enjoy using each of these lenses, but for different purposes.