humm, I was thinking about it differently. I would expect most pumped storage to have variable and diminishing cost per MWh (up to a point). Part of this is the turbines, but also other fixed project costs and economies of scale. If you hold MW fixed, the First MWh of the project is going to be more than the next until you hit diminishing returns due to specific site saturation.

As an interesting side note, China has roughly 80 GW of pumped storage built or under construction. Most of the big ones I have looked at are about "10C".

This is comparable to the GW output from their nuclear reactors built or under construction.

Tangent: have you been following the Medog Hydropower Station? https://en.wikipedia.org/wiki/Medog_Hydropower_Station