A 2014 Ford Focus gets ~40mpg. Assuming 12,000 miles/year, that's ~300 gallons of fuel. Assume, conservatively, $3/gallon. That's ~$900/year for fuel, or $2700 over 3 years. The cost to get supercharger access from Tesla is $2000 at time of purchase ($2500 after delivery).
To finance $2000 at even a ridiculously high 10% over 3 years is $64.53/month, fully loaded principal and interest. This is already less than most people pay per month for gasoline/petrol.
And that's THREE YEARS. After that, to fuel at Superchargers is essentially free (already amortized).