I use approximately half of my 80% charge (capped max charge limit at 80% total capacity) 5 days a week, with less use on the weekends. When I first got the car, I had not switched to my local PG&E's tiered rate plan. I simply used "off peak" hours (6pm to 5am or whatever). My monthly bill went from about $200 to over $500/mo. After switching to tiered rates, my monthly bill is now down to ~$300. That said, Ive only had this car for 2 months, so this is a very limited cross section I'm drawing from. I should also note I exclusively charge at home. I've used a supercharger a total of twice.
What was your gasoline bill for your drive before you got your S?