I have a vague memory of paying about 5 or 6 euros for a character photo. We paid more than this for a family photo taken on Main Street with the castle in the background (but it was nice!).
Someone may well correct me on these prices.
The only down-side was that the collection process (in the Studios) was slow. You had to line up and wait and then they scrolled through every photo (displayed on computer screen) taken with that character until they find yours. It seemed to be a slow way of doing it - plus one of ours (Mr Incredible) went missing If you have the patience to wait - they are worth it. But remember if you don't wish to pay for lots you can still line up and have your picture taken with the character and use your own camera to take your own picture - you are under no obligation to buy (or even look at) the professional picture.
That is good to know. We are only planning to buy one or two official photos of our group. For the rest we will take the pictures with the characters with our own cameras.