I don't know how much it actually costs, but taking the numbers here at face value, $1000 over 200,000 miles is half a penny a mile - that is clearly trivial compared to running costs of any car. One way to look at it, is if you assume $3/gallon gas and 50 mpg, then the cost of the battery is equivalent to reducing the gas mileage to 46 mpg, all else being equal.