we have this book and i would not pay $25 for it. you can sometimes find one at a good used book store for about $5. also i bet you could get one on ebay or another online auction site. my first choice to find used (or new) books is Powell's Online Bookstore. The real store is in Portland Oregon and they have EVERYTHING! The store is like 4 blocks long and has several floors. great way to spend an afternoon just exploring and finding all kinds of neat books.
I have a copy of the book & map set and really like it. I ordered it by phone from Princess well in advance of my trip so that I could read it ahead of time. (I'm not going on Princess.)
I think it's worthwhile. It covers quite a variety of information including history, things to do, fishing industry background, detailed descriptions of the cruise route and sights, lots of interesting photographs, wildlife information, Alaska Native Americans, etc.
The included map is very similar to the one you get for free with a Princess cruise book. However, it has more detailed scale (1 inch = 24 miles versus 1 inch = 68 miles). The map is numbered with "mile markers" that correspond to the text in the book.
For more information see <http://www.alaskacruise.com/Books.htm> Be sure to order the Northbound or Southbound edition depending on your cruise plans.