Figure with your current electric rate what 8 KWH cost. That will take you about 35 miles in the Volt. Ask your electric utility if you can get a discount with a 240 V charger used only at night. Can you charge at your destination, say work, every day and how much?
For me at my current $0.07 KWH rate during the day and using $3.50 for a gallon of gas. I would increase my electric bill $11 a month but save $156 in gas a month. I believe I can get a lower rate if I charge only at night. My employer is installed 240 V charging stations that are free. So it is possible I may save an additional $11 per month.