Anybody familiar with Knee-Deep in Thunder?

I just posted this same question in the booksellers group, as well. I recently received a nice first edition hardcover of Knee-Deep in Thunder by Sheila Moon at my bookstore. Dust jacket's in fine shape. I take a look and see that it is signed by the author. When I looked on ABE, I found two similar copies signed, one going for $75 and the other for $100. Can anybody give me an idea why this relatively obscure (at least to me) author's signature would make this book so highly priced? Thanks! I want to price it fairly.

I don't know why the price is so high, but that was one of my favorite books as a young teen, and I don't think it was in print for very long. Maybe there is a following.

Thanks, Liz. Maybe the people pricing it so high love the book, too, and don't really want to sell it!

There are other signed Sheila Moon books out there at much lower prices but they seem to be mostly paperback and mostly from later years. Knee-Deep appears to be the foundational book in the career of a well-loved author; and it's a hardback of the first book in a series, published almost 50 years ago, probably in a pretty small printing. The small printing, along with many of the copies being read to pieces or library-ized, means that nice clothbound firsts of this are likely pretty scarce. Combine that with the significance this book has for many people, and the small supply/high demand translates into an elevated price. At least that's how I read it...

Thanks, Bill. Good information. Given all that I find it strange that I was unfamiliar with Moon, as I have been an avid reader all my life, including throughout my childhood.