I got a copy of this book at a book sale many years ago. I wanted to purchase more of them to pass along to my family because I loved it so much, that is when I discovered that it was being sold for over $100 (http://www.amazon.com/gp/offer-listing/0876143834/ref=dp_olp_used?ie=UTF8&condition=used)! Can any one tell me why this book is worth so much? Thank you!