To broaden the inquiry but stay with that same design, there is also the Sc. 322 horizontal coil (perf 12 vertically and not 12 1/2 which is a private perf). The 322 is also rare, but not extremely rare as the 321 and not as costly.
Not quite what I would call a poor man's alternative, but one can have a 322 without taking out a 2nd mortgage. There is one about to go under the hammer at Siegel toward the end of the month. When you use Siegel's PowerSearch you'll see the recent history would suggest a single runs $2K to $ 3K, and a pair will run $3K to $4 K.
I do not see a hint of a census there of surviving 322, but one could probably approach this by searching certificate databases to get a lower bound and thus a bit of an idea. There are a dozen in the last ten years at PSE, which we can search thanks to Don's efforts (see
http://www.stampsmarter.com/Learning/PSEView.html). One or two of these might be the same stamp, of course, so one would need to guard against overlap....
Are there perhaps 3 or 4 dozen? Might be a fun project for someone. Although perhaps it's already been done. Anyone into coils know?
[Edited to add that in another Forum thread Russ indicated in 2011 there were 167 certified instances of the 322, most being pairs.]
Since we like images, here is another one that is now offered on Hipstamp.
