One more worthless story while I'm at it. I once saw a bone colored hard ark stone (my favorite - where's the hearts on this site so I can show how much I love them?). It was on ebay, and the back of it looked hand cut. There's no particular value in old arkansas stones above and beyond new ones, though, unless they have a vintage pike level.
The stone was dirty, and the seller who listed it listed it for $200. I thought that was pretty rude (yeah, I know, who am I to judge?). It's about 8 inches long, a little less than 2 inches wide - typical vintage bench stone. So I did what I often do with places that have BO sales. I sent them an offer for $100 including shipping figuring they would get in a huff and we'd go our separate ways. It took less than 10 minutes to get a response back that they accepted my offer, they sent me my stone and I friggin love it!!
It's the bone stone in this video. I'm glad I made the offer. Someone else made me a box for it as a return for a favor, it's a nice little unit now, but I don't use it for razors (it would work fine for that if I lapped the nicks out of the corners, though).
https://www.youtube.com/watch?v=G85B6iVCyMo
If that guy has BO options on his site, and he does have nice stones that someone wants, never hurts to send offers for what you think the value is.