Kay prices are all over the place. An M-1 from the early 50s in excellent shape can sell from $1500 - $3500. To get a better idea, check the Kays in our FS section, ebay's sales history page, and places like
www.fretwellbass.com. There are lots of M-1s out there.
I don't think any serious orchestral player will have any real interest in this. I'm a Kay owner (1939 S-8) and love mine, but would not use it for orchestral work.