Just checked the trip meter on the Tesla S today, we did 20000 kilometres since purchase in June 2015, most of the driving distance covered was through the past winter.
Averaging 230 Wh/km over the past 20000 km = 4600 kWh of energy used
~3000 of those km were on free superchargers provided by Tesla.
The remaining 17000 km * .15 / kWh (overnight electricity) = $590 in "fuel" (fed at 24Amps/245V charging every night for an hour or two on average)
Mid grade gas (what we put in our Mercedes SUV) averaged $1.16/L in 2015, ref:
http://www.energy.gov.on.ca/en/fuel-prices/?fuel=MID&yr=2015Our 2010 Mercedes best efficiency was 10L/100km in (left lane) highway conditions, and 13L/100 city year round.
Our old Ford sedans averaged just a bit better than that, about 10L/100 year round.
$590 / 1.16 $/L = 510 L of gas which would have been good for around 5000 km
20000 km would have been $2000 in gas in any of our previous cars.
Savings of ~$1500 in fuel in 8 months of driving compared to the gas car the Tesla replaced.
Not bad!