I wouldn't interpret the relatively low cost of the 210/4 ULD in the used market as a sign of something lacking in performance. I think it's more to do with it being "sandwiched" between the 200/2.8 APO (more desirable for ultimate image quality and speed in this focal length) and the 105-210/4.5 ULD zoom (that 1/3rd stop difference is negligible, it also has ULD glass, it's also AF, and well, it's a handy zoom).
How important is AF, really? Cats tend to spend a lot of time keeping quite still, do they not?!
FWIW, I use the 200/2.8 APO on my 645AFD, and I don't really miss AF or auto-aperture. Since I usually shoot it between f2.8 and f5.6 and set it to "M" so that it's already in stopped-down mode, it's still bright enough to focus, it gives focus confirmation (f5.6 is the limit), and I don't need to reset anything on the aperture or change a stop-down switch before taking the shot. Compose -> confirm focus -> fire.
Being a "dumb" lens on the AFD, it will work equally well with an extension tube - including an "AF" tube (I have the thinnest, #1 AF tube) - for closer focus.
With the 2x N converter, it's also a fine 400/5.6 lens.
Ray