I ordered the Bruce Davidson print for my signed copy of East 100th St. which is already selling for around $400-$500 without the print. I really need to insure my book collection...it is
seriously getting up there...
There are so many editions, hard to know which to buy. The first edition from Zürich: Conzett & Huber, 1969, is seldom offered signed, but the Harvard University Press edition is nicer anyway, and as you say is getting up there, $175 for mint unsigned copies. Signed copies of later editions are still nice, and a bargain IMO.
However if I wanted a print, honestly I would spring for a larger print. Beetles and Huxley for instance currently have a half dozen much more interesting prints @ around 4000 USD. One can often do much better at auction on his work.
I have a small Lurie Simmons, "Jimmy the Camera," and often wish I had purchased the larger size. 6x6 is really small.
The two questions that need to be asked are: 1. How many of each print will be issued? Is it an open ended print run? and, 2. How is the print produced? Different productions have different values?
Personally, I suspect that if you are interested in the particular work of a photographer purchase a signed copy of one of his books. They often have limited runs.
The little prints are just for fun, but you are right. If one is shopping for a particular image in a larger size, prices will vary wildly, you really have to do your homework, and not be in a hurry. It is not unusual to save 50% over commonly advertised prices. I would not buy from Magnum, but would buy from a dealer.