I bought a used 2014 SL with 40,0xx miles on it, and 11 bars on the battery about a week ago.
I just did the math on the cost of driving my Nissan LEAF, and I am amazed. Over this last week, doing normal driving (commuting to and from work, picking kids up from daycare, trips to the gym, grocery store, and church), I averaged 4.3 miles per kWh.
Puget Sound Energy charges $.09/kWh for the first 600 kWh, and $0.10/kWh after, each month. Right now we average just over 600 kWh/mo. So with the added expense of charging my vehicle, I'm guessing it will add to the $0.10/kWh rate on my bill.
At 4.3 kWh/mi, this means it will cost me about $0.023 or $0.024 per mile to drive my LEAF. With gas being (conservatively) $3.00/gal right now, for me to get down to $0.024/mi in cost (that's 2.4 cents per mile), I would need to get around 125mpg with a gasoline engine.
Compared to the 11mpg truck I was driving ($0.2727/mi in gas), at about 10,000mi/yr ($2,727/yr in gas vs $240/yr in electricity), I’m saving about $2,300 in gas alone!
TLDR: I'm getting the equivalent of 125mpg in my electric car based on current electricity rates and fuel costs in my area.