The first thing I did was search Google for Disney clip arts for the kids' favorite characters and saved several different ones if I knew more than one kid like that character. Then I used Pages to set up an 8x8 border. I have a Mac and Pages was awesome for this. You can do the same thing on other graphic apps for PC too.
I situated the 8x8 border toward the right with about half an inch margin on the 3 edges (right, top, and bottom). I then just dragged one character clip art and put it in any corner that looks good. For some, I also put the name of the character somewhere on the page. But because did this days before I trip, I ran out of time and just put the characters. For other ideas, you can also get seasonal clip arts - Christmas, valentines, etc.
Once the pages were set up, I printed them on stock paper. I grabbed several packs at the craft store. Although , I advise you pay attention to the thickness, as some are thicker than others. I fed the paper one at a time because it's thick and I didn't want to have to jam the printer.
After printing about 10 characters for each child (many are repeated), I also made 3 blank ones for each (only the 8x8 border) for any unexpected character encounters.
Once the pages were printed out, I hopped to the car and hurried to Staples. We were leaving the very next day, so you can imagine the panic I was in at this point. I told the Staple lady I wanted 4 booklets bound and she gave me a choice of the binding. I picked a spiral and a clear cover. She out a clear front cover and a thick black board on the back. I had to tell her to trim the left side as it was about 2 inches from the boarder. At this point I told her that as long as she didn't touch the black border, she could trim whatever was needed for the spiral.
For all 4 (14 pages each - I made a cover with each child's name) I paid $17. Pretty awesome, I think. :)
Each of my 4 kids had a small cinch sack with them with their own autograph books. I kept the sharpies. The corners curled in, which was not a problem because of the 1/4 - 1/2 inch margins.
While at Disney, I saw a scrap booking kit that I bought for $25. It had a lot of the mainstream characters. Once we got home I ordered 8x8 scrapbooks (with top loaded protective sheets) from Amazon. Once I got them, I cut out the autographed pages on the boarder and they fit perfectly inside. I added stickers, boarders, etc from my Disney scrapbook kit. I am actually not done making them. I want one page to have a picture of my child with the character and the page next to it, the character's autograph. I anticipate these scrapbook to be handled pretty good, especially by my twin 5-yr olds. :)
The great thing about this DIY autograph book is that the pictures you print on the page is a "conversation" starter with the characters themselves! Mickey was beside himself seeing his picture, and so was Ferb (from Phineas and Ferb). We had a great laugh at him running around and showing everyone that it was him on the page. The kids loves the antics!