Saw one for sale at H.H. Harris, near the Chicago PD building in 1965. Wish I had bought it, but that applies to a lot of things and I didn't have any money in those days anyway. Don't know if the firm still exists, but at the time it was the big police supply outfit in that town. The M45s are scarce by any standards. As I recall the USPS bought some as training pieces. The Jinks book mentions them.
Unless very well used they are pretty collectable. Essentially they would be very similar to any of the other K frame .22s, such as M18, K-22, etc.
I have always liked the idea of .22 caliber understudy guns but for some reason the Model 45s never caught on.