less than $10 – a fifth of the price of gasoline
Only because gasoline for road use is taxed much more than electricty. At present.
a matter of how quickly you could get the energy into the car
Which is one place where flow-technology batteries might actually be useful. If recharging became simply a case of draining the used electrolyte and refilling with fresh, refuelling could be as quick and easy as it is today for gasoline vehicles. Small filling stations could be refilled by tanker using a similar system, larger ones with good grid access might have on-site electrolyte recharging facilities. It would be interesting to see numbers on fluid quantity versus range.