Book galleys are also called "bound galleys" and are the bane of my existence. It is an author's manuscript after it has been copyedited and typeset. It is usually (unless I have no time to do so) the already-proofread pass of the interior. The typeface and design are usually final (they have to be before the pages are run out), although the front matter (title page, half title page) may not be. It will not be the final copy of the book that is released in bookstores.
Bound galleys are put together for several reasons. They are given to our Sales reps, so they can pass on to accounts for review, so they can decide whether or not they want to carry a book in their store. They are given to reviewers, so we can get quotes for the jacket, or to solicit reviews in magazines. And sometimes they are given to authors for talking tours.
The neat thing about galleys is that they are not the finished copy of the book, and if the author is huge, can be worth a lot of money in the future. Harper Lee's bound galley for To Kill a Mockingbird sold for A LOT more money than the first edition, first printing of the finished book.
The thing I hate about galleys and people selling them online and in stores is that galleys are NOT TO BE RESOLD. They're free; the're just not public. Our galleys are paid by the company but given to our accounts for free. Wait long enough and bound galleys will show up on our freebie shelf for the taking. If you go to the Book Expo of America, you can get as many of them as you want for free. But if you really like this author, and it's less than two bucks, sure, get it. You may not get it any other way, and you'd have it before everyone else. Just keep in mind that the text may change (I've had authors who have changed entire scenes before final printing), so it's not truly final.
I wish I knew which book you were looking for! It makes me angry that someone would charge you for something they probably got for free.
Managing editor at large