I bought a couple of 22/45s in the last couple of years - both used MKII variants - one was close to the price of the new one above and is also a 5 1/2" bull but is stainless and factory drilled and tapped like the new ones. The other I picked up for $200 with box and paperwork , it is a 4" bull. I was out shooting it today.
Very good deal! I bought a 22/45 mark III several years in the same configuration for slightly more. It is more accurate than I am has worked flawlessly for over 5k rounds. I only wish it had the easy takedown like the Mark IV