Desalination would also work well with (future) cheap photovoltaic generated electricity. It'd be a perfect use for overproduction of electricity since the desalinated water can be stored easily.

That's $4B for construction and $1.5B for operating costs over 25-30 years. Let's say 25 years to be conservative. So $220M/year.

It's expected to produce 150B liters/year. That's $0.00146/L or $0.0055/gal.

Imagine switching to solar doubles the ongoing cost. This is conservative since solar isn't that much more expensive and there are costs other than electricity, but lets go with it. Then the cost goes up to $280M/year and we're talking $0.007/gal.

That's really very cheap.