Currently, as everyone knows, Turbine will be selling the expansion with the Epic Questline as part of it.
In my opinion, another good way to implement this into the store would be:
Helm's Deep-Road to War Cluster
-Access to the Epic Storyline throughout the Helm's Deep Expansion
-One time usage of the Epic Battles required to complete the Epic Storyline*
*The "One time" usage does not off any rewards(Meaning people will still have to get Epic Battles) and the limit is not taken off until the battle is completed.
This means that players can still complete the epics for a cheaper price(900tp, anyone?), and it might even lead to them eventually buying the expansion, if they like the little taste of Epic Battles provided.
Thank you for your time,