The battery pack costs more than that, alas. The price may come down as the scale of recycling (and hence, the amount recyclers can pay for used batteries) goes up. The price per Wh for Li-ion has also been falling at a fairly steady rate. And of course, gas prices may go up.

We should also consider the depreciation of components in a conventional car that the electric drivetrain replaces. They should depreciate faster because they are less efficient and must deal with the additional heat they dissipate. They require an intake and exhaust system, complicated transmission, pumps, valves, lubricants...