A pumped storage installation is under consideration in Colorado. The cost estimate is interesting:

Pumped-storage hydro projects cost about $2,000 per kilowatt to build, according to the National Hydropower Association. (That compares to about $1,800 per kilowatt for utility-scale solar and $1,400 per kilowatt for onshore wind turbines.)

Of course it is difficult to make a direct comparison between a source like wind or solar and a storage system, but the need for storage is also pretty clear.