Mark's involvement in college-level pool instruction could be part of the reason this book looks, and reads, like a first-rate college text.
I bought mine when they first came out. I paid more for the each of Eddie Robin's one pocket books, and almost as much for some lesser instructional materials, so I didn't think the price was too high. It's not cheap, but it is not a cheaply made paperback.
Mark's book is heavy slick paper, hard cover, well bound, full color on many pages, autographed, and mine shipped in a protective box. To me it is a book to be read and handed down to an interested party, or donated to a library, rather than ending up in a garage sale.
Depending on future reprints, I expect this book to retain its value for a long time. Thus, for those who think it is expensive, you can buy it, then read and study it for awhile. If you choose to sell it you'll probably get 80% back, making the use of it almost free. Or you could get it stocked at your local library.