Cost of electricity
The average price a residential customer in the United States pays for electricity is 13 cents per kWh.
So if you want to completely charge a the battery of a Tesla Model S Long Range (100 kWh), you would pay $13 for the electricity. This gives you a range of 370 miles.
If we compare this to a regular gasoline car with an average mpg of 36 and a fuel cost for regular-grade gasoline of $2.50 per gallon (march 2019), we would have a fuel cost of $25.69 for the same distance.
So it’s roughly two times cheaper to drive a Tesla than a regular gasoline car when you charge at home.
Note: if you have solar panels on your house, you can basically drive around for free (if the capacity is sufficient).
Tesla’s are also cheaper to drive thanks to the lower maintenance cost. You don’t need oil changes, transmission fluid, timing belt replacements, etc. And thanks to regenerative braking, the brake pads last much longer.