Yowch_ wrote (Google translated):
Will I be billed for the price I pre-ordered or the increased price?
I recently requested a pre-order for a movie on the apple tv app and today the purchases and rentals increased. When the pre-order is active will I be billed for the price I pre-ordered or the increased price?
Interesting. I have not seen that happen before. I would assume that the supplying studio can set a price and stick to that, at least from pre-order announcement to release date.
Please contact the iTunes Store staff for specifics on your pre-order title and its price. They should have an answer to this.
(If you want to cancel your pre-order for any reason: View or cancel pre-orders for apps, movies, music, or books - Apple Support)