Who knows? It is all crazy.
Less than a year ago I had an immaculate bolt-modded 1992 blue label that I tried to sell here and on ebay. I started at $100 and after several weeks of steadily dropping prices, I finally sold it on ebay for about $55.
Having owned a couple of dozen Model Ms of all ages, I can tell you that there are distinct differences but still within a rather narrow band of variation. If you have never used buckling springs, buy a Unicomp with native USB and Windows keys. If you like "classic" and/or "collectable" stuff, there is tons of classic IBM hardware out there.
The parallel thread "Thinking about buying a Unicomp" shows just how wild it has gotten.
But that is all moot. After moving past the neophyte stage, anybody who is serious about using buckling springs is probably on a Model F.
Flame on, haters!