Increased END Cost Only To Activate

[Zed-F]

Increased END Cost can be quite a significant limitation, especially when bought to high levels. However, sometimes it might be appropriate for a character to want to have a power that costs a substantial amount of END to activate, but not to maintain. In these cases, we might wind up with a power that costs 10 or 20 END to activate, which could potentially be done outside of combat time when END is not an issue, then maintain the power indefinitely including into a combat situation, and still get a huge limitation on the power. What is the appropriate mechanic to represent this?

Buy Increased END Cost normally.
Use the "Only In Certain Circumstances" rule. In this case, is activation considered a Very Common, a Common, or an Uncommon circumstance? It occurs exactly once per use of the power, regardless of how long that power is up for.
Halve the value of the Increased END Cost, mirroring the relationship of No END cost to Costs END to Activate and Costs End (every phase.)
Something else?

[Steve Long]

A character may apply the Increased Endurance Cost Limitation to a power that Costs Endurance Only To Activate (whether due to an Advantage or a Limitation), but he only receives half value for the Limitation. (The GM may also allow this for other powers, if desired, but may wish to reduce the value of the Limitation further.)