I bought mine online as I like to have them before we go and as soon as we are there (our second trip we missed out on some great, unusual autographs because we hadn't had a chance to buy them when we arrived!).
But, someone said they are 9 euros in the park so slightly cheaper to buy over there at the moment with the exchange rate. Plus you have to factor in the extortionate (imo) Disney Store shipping rate. I was lucky that I was ordering other things which gave me half price shipping so didn't miss out.
HTH
BTW- the book doesn't have as many pages as the usual books as there is a slot/photo pocket on the each opposite page for photos. Not a problem for us as I doubt we'll fill the whole book, but if you were a keen autograph hunter and going at a quiet time you might find one book isn't enough.
Dreams Unlimited Travel is committed to providing you with the very best vacation planning experience possible. Our Vacation Planners are experts and will share their honest advice to help you have a magical vacation.