I don't think that it is more rare than an equivalent space saver.
These things turn up regularly, and considering supply-and-demand, the demand will always be low because it is such an uncomfortable and inappropriate layout. IBM knew it, too, they did not make these for long before they totally changed the design - twice.
In that case, you haven't been paying attention to guy selling them NIB on eBay for the last 2 years or more !
He sells one of these 'rare' keyboards for about 300$ and magically, he has one more.. and one more.... and one more ......
You don't even see that many NIB Model M's on eBay !!!
Also : Screw 'supply and demand' and all that marketing-mumbo-jumbo , these items are in line to become 'of historical interest' .
It doesn't matter that the layout suxx, it suxx less than most other keyboard-layouts at the time AND it's an 'evolutionary steeping-stone' towards the layouts we have today,
layouts that ALSO SUXX ..
"QWERTY" OR CHAOS !!
![IBM Model F XT on ebay - top shelf, top dollar](https://geekhack.org/index.php?PHPSESSID=v8v6gbosulld6loobair9ftp5g6uhbb2&action=dlattach;topic=42758.0;attach=20153;image)
We are STILL using a inferior layout .. To prevent what you see in the photo above !!