Lets say you buy the book. Even with "all hands on deck" during 10.01 to 12.31, I see a 10 to 20% drop in the book before next summer. If you are set on buying this book, I would make a downpayment. I would then structure the deal in such a way that you analyze the book every 6 months. Future payments would be tied to the books retention.
Good advice. This would be the only way to buy a book.