5 miles per kWh wall-to-wheel is probably a bit optimistic. That might be right for the number from the battery to the wheel, but there are charging losses and other overhead that uses some of the electricity you pull from the wall. Both our Tesla Roadster and RAV4-EV get about 0.320 kWh/mile. Our electricity cost is $0.11/kWh, so that comes out to about 30 miles per dollar of electricity, or about 90 miles for the cost of a gallon of gas.
In short, you don't have to worry about how much your electricity bill goes up, because that will be more than offset by the money you save from not buying gasoline.
If you're worried about being able to pay your electric bill, every time you do a charge put money in a jar equal to the cost of gas to travel the distance you drove since the last charge. For example, if your gas-burner gets 25 mpg and gas is $3/gallon, that's $12 per 100 miles of driving.
Do that all month, then send one third of it to the electric utility and use the rest to throw a party. The more you drive, the bigger the party.
If you're worried about the cost of replacing the battery pack in 5 to 10 years, then instead of throwing a party every month on the extra cash from the jar, deposit it in a savings account. Throw in $30 every three months for the oil change you don't have to do, plus another $100/year for engine engine/muffler/transmission maintenance you don't have. Add a little in interest and you'll have over $10,000 after eight years of driving 12,000 miles per year, which should be more than enough to buy a replacement battery pack. The electric motor and gearbox should last much longer than an engine and transmission, that should cover all of your drive train costs for 8 years, with enough left over for a nice party.