I pay £9.99 a month for a NOW TV Entertainment Pass. (I've got a NOW TV Stick, which is no longer available to new subscribers. You now need to have a separate device, such as an Amazon Fire TV Stick, a Roku device or a BT TV box, to receive NOW TV services).
As I read it though (from my link above), the NOW TV Entertainment Pass is included within most BT TV packages. So, if you got BT TV, you wouldn't have to pay extra for it. However if you wanted other types of NOW TV 'passes', such as their Cinema Pass (which gets you all of the Sky Cinema channels, plus loads of 'on demand' movies too), you would have to pay. (The Cinema Pass costs £9.99 per month).