As for a value, I’m not an appraiser; but I do suggest doing searches of online auctions as that will give you some clue as to the market value. If, however, you cannot find a card like yours (or, in other cases, any item you have cannot be found), the next steps would be to contact collecting groups to see if they have any idea. In this case, both ‘horse collectors’ and ephemera groups, even book collectors, would be good places to start. In many of these cases, they won’t be able to give you an appraisal either — but they may have ball park values based on their experiences.

If you want a ‘real value’ then contact a professional appraiser or auction house with such services — such as Ivey-Selkirk http://www.iveyselkirk.com/ They do this sort of thing all the time — and are much more reliable than a (jealous) schlub like me