Here is simple example:
SR+
Lets say price per gallon of gas is $2.5
Lets say price per kWh 15c
Let say I have Tesla SR+ and Honda Insight
Honda Insight real life MPG is 50 this means 1 mile costs me $2.5/50miles = 0.05c
Tesla SR+ real lie MPGe is 140 or 130? whatever, it doesn't matter anyway, Real Life SR+ MPG is 60:
180 real miles(out of 250 advertised) divided by 3 gallons I can buy on 50kWh energy cost (50kWh*0.15c=$7.5/$2.5 per gallon=3Gallons of gas price to charge SR+) = 180 / 3 = 60 MPG
Why 180 miles? Our Saint Elon said 250miles!!!!111 This number from my own experience from driving over 16k miles, and also from this person's post as additional supporting documentation:
180 miles of reasonable range M3 SR+ — Tesla Forums
"because the 240 mile range is only achievable under unrealistic conditions."
Thank you for your time.
PS. price on supercharges ~double of those 15c, so MPG will be 30, which is lower than most of modern cars in the same car class.