Right now, batteries for a realistic replacement car (not a compromise EV like a Leaf) cost about $20,000 per vehicle. That's $10 trillion for 500 million cars. It doesn't look an order of magnitude smaller to me.

As for where the money comes from, doesn't that just fall out of supply and demand? As demand for electricity increases, prices will go up, funding the infrastructure improvements needed to accommodate the increased demand.

The solution may not even lie in the grid. Batteries can solve the grid problem as well as the battery problem. Give every electric car customer enough solar to cover his charging needs and a fixed storage installation to keep the power for when the car comes home, and the grid won't even know the cars are there.

I'm sure this will all be wonderfully challenging for those involved, but it doesn't look like something to worry about from the outside.