I also made my own. I actually printed character-specific pages using images that were posted on the creativs DISigns thread. I printed two per page, cut the pages in half and had it bound. So, my book is 5.5" tall and 8.5" wide, with the binding on the left side. It costs less than $5 to get it bound at an office supply store. I would recommend spiral binding because the type I used... the pages fell out every time the character flipped the book completely open.
You could just use colored cardstock and not even do any printing. Make a custom cover, and there ya go! Then, you take a picture with each character and adhere it to the page that's facing the autograph. Instant souvineer for cheap.