In comments, Adam points out that EEStor originally claimed to be able to sell storage at a cost much lower than I was taking as an estimate. This was part of my whole "conservative estimation" thing, but if we throw caution to the wind and assume EEStor can hit the $2100-$3200 price point and that we only need 12 hours of storage, that gives us a $/watt figure of about $3.90/watt, about what new coal plants are costing in the States these days. Or about half of what new nuclear is costing.
To reiterate: if EEStor's claims are legit, renewables can provide baseload power at a cost equal to coal, and cheaper than nuclear.
It's all napkin-doodling at the moment, but I like to point this stuff out because at the moment we're planning on a 30-year timeline at the exact moment when a lot of our assumptions are going to be proved invalid.