They'll more than likely re-release the ebook for $12.95 when the film comes out and with a new cover showing the stars and/or the usual Stephen King blurb, along with some half-naked man (waist up) staring slack-jawed at some demon wearing a mini-skirt. They'll sell 500,000 copies - if the film is successful.
The alternative was not very pretty: Sell 758 copies for $2.98 (or whatever the price was before the film was negotiated).