There are many estimates for the generation cost on wikipedia, at least the IPCC one does not try to estimate what the costs of the emissions would be.

And the price of the battery does obviously not include the generation costs of the energy needed to charge it, any charging/discharging losses, nor the infrastructure costs of a V2G setup.

So it's a very simplistic and incomplete comparison that gives a rosier picture of V2G MWh price than reality would.