For a serious poker book, this isn't the most expensive I've seen. Shootaa (Reid Young) has a book out for around $5k and when it came out it honestly may have been worth the price. The fact is that these tips will allow you to improve your game so much that you'll make more than the price of book in a relatively short period of time. Granted, this is assuming you're already a mid-high stakes player (or for the case of this book, small-mid stakes).
Previously, and this is probably still the case but I've stopped playing because of Black Friday, the best ways to learn were to watch training videos, learn through forums such as this one, and discuss hands with players who are better than yourself. If you still have a lot to learn, books like these may not help you much. But at the end of the day if you're struggling at 100nl with a 2bb/100 winrate, this sort of book could potentially help you quite a bit.
I confess that I have no knowledge of the book you've mentioned but decided to answer the more general question of why poker books can be so expensive. Another poster mentioned that books from well known (and he would argue, more credible) poker pros are much cheaper. The fact of the matter is that these books are
a) severely outdated
b) written mostly by live players who have little to no experience playing online
c) written by players who are famous and not necessarily skilled
Doyle Brunson is obviously a great poker player; however, I'd much sooner take the advice of a winning 400nl reg than him when it comes to online (and possibly live, but that's another argument) games.