As far as the 'Preview Weekend' goes, the cheapest you can get it is gunna be £178.20 each for two people, based on using a 10% annual pass discount.
I checked this with Alton Towers and they've backed that up and also said that the Friday and Saturday nights will be dedicated to talks from people involved (John on Sat night), and Saturday day time for the behind the scenes walkaround shizz.
They also said "If you decide to book, best to do so on the basis that it is a behind-the-scenes/social event weekend without rides.. that way you won't be disappointed."
It's expensive, but then again it is a weekend away including meals, and John Wardley!