Where can I find the value of 100 yr.old books?
You can take it to a rare books dealer for an appraisal (which may not be free) or watch for someone to sell the same or a similar book online at ebay or elsewhere. Most books that old sell for about $3. Yes, in good condition. Yes, leather-bound or cloth-bound. Yes, classics still being printed and read. It’s sad, really. There are, of course, exceptions, and you’d be wise to determine whether the books you have include any exceptions. You may well find that the old books are more valuable to you as possessions than the money you could get for them. Old books are cool.