The 2018 Mercedes-Benz SL 550 is available as a 2-door, 2-seat convertible. Starting at $112,300, the 2018 Mercedes-Benz SL 550 Base is powered by a 4.7L, 8-cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 25-mpg on the highway. The top of the line 2018 Mercedes-Benz SL 550 SL 550, priced at $112,300, is powered by a 4.7L, 8-cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 25-mpg on the highway.