My electric rate is is 7 cents a KwH, compared to 25cents which is what I believe the average Supercharger rate is.
I will have to upgrade from 100 amp service at home to get to Level 2, but I've decided to hold off because I only commute to a nearby train whose garage will get me free level 1 charging. That's about 10 hours a day. When the car is not there, I will plug in at home form another 8-10 hours.
My workweek is 4 days, so I imagine I might have to hit a nearby supercharger once a week or two. Depending how that all goes, I may not even have to put the Level 2 in at home. Upgrading the electric service seems really pricy.