[tcaud]

Battery Junction is selling 3.7v Li-on batteries with 0.7ah each for about $5 apiece.

To get to Tesla level you'd need 100 of those, which would produce 70ah at 370 volts for 26khw (about 80 miles).

Of course the super/composite battery is only guaranteed for 500 charges, but it is also very, very light. You'd save tremendous mpg on account of the lightness, or so I'd think. You'd be looking at $500 for the base cost (although you'd have benefit of volume so maybe a 30% discount), then the wiring/management and cooling (which I figure could be done with coolant and insulation).