If you have to ask ....
Anyone buying a new car, any new car, let alone a luxury car, to "save money" misses the economic reality. Look at ads posted on this forum for cars a year or two old: most have cost from one to four dollars (or more!) per mile in depreciation alone.
The ugly, literally ugly, truth is that the cheapest transportation per mile is a battered fifteen year old car with over 150,000 miles. Large or small doesn't matter because no matter how good or bad the fuel economy they'll only cost between a nickel and a dime per mile in gas and suffer no depreciation.