I kind of got lost in your calcuations. For me, a 240V at $500. is more of a convenience. But, what I have found is that the 240V charger can help during the mid day where you could get more eMiles without using gasoline. And, gasoline is 3x + more expensive than electricity.
For others, you can use 240 after work at home. Charge it a little and get another 20-40 miles to go out for dinner, errands / shopping, etc. On weekends, you can got out for breakfast and return, charge up for 1-2 hrs, go out for groceries, charge up, get a movie, charge up, get dinner, charge up. You probably can pull off a 80-100 miles day all on electricity with a 240V charger.
On the other hand, if you can find a way to get a ROI after 3 years on $500 just on your electricity schedules, then I think a 240V is a way to go. I think you will get better gains from the convenience and those busy days that you can rest 1-3 hrs to get a little more charge for what the rest of they day has in stored for you.