I have bought small spiral scrap books from Hobby Lobby to use as autograph books. They are 4x5" and have maybe 20 pages. They are cheaper than the disney autograph books and I like the spiral because you can open the book to a page and the character won't have to be fumbling around with pages closing on him. THe pages are more like card stock and easy to write on.
When we get home I paste a picture in the book of DD with the character on the page next to the autograph and she has her own mini photo album of the trip. It works out great.