It varies- lots of factors, including when it was signed timeline-wise. His "early": signature was different than the later years (I have one of each)- generally, you can figure $3500-4500 for a good quality "cut"/index card- in the past several years I have pivoted away from the balls, bats and photos to "Personal Checks". I have a couple of hundred of those as well, from Edison and Einstein to Wrigley and Lombardi. Right now, I have my eye on this one: https://www.cleansweepauctions.com/item-697894/
I have done business with this outfit (based here in LI) for 20+ years- they are the best. However, if you want to get a feel for the auction value of an item, sign up at Heritage https://www.ha.com/ They are the biggest, and you will see plenty of Ruth's on any given weekend auction for comparison sakes. In the meantime, here's another of my faves - I'm on the lookout for Wilbur's LOL
The Law (f/k/a emz)- Keeping the Streets and Gutters of Gotham and Penny Land Safe since 1980-something.TM*