The 2.0 update itself is absolutely free to existing customers. Along with it, the new interface, the new editor, the iPhone 6 support, the ability to mark reminders complete or defer them from notification etc, on top of everything else that Due already had.
There are four extra features that are unlocked with an optional in-app purchase (Upgrade from 1.0). At the time of writing, the price is $2.99 on the US App Store, which is 40% off the full price of Due 2 when purchased new.
Otherwise, you can enjoy the updated version of Due without paying for anything.
The four extra features are:
- 5, 10, 15, 30 mins auto snooze (previously only 1 minute and 1 hour)
- Background sync with Dropbox
- Access to 45 new tones
- Ability to pause and resume your timers