The 2017 Mercedes-Benz SL-Class is a 2-door, 2-seat Convertible, available in 2 trims, ranging from the SL550 to the Base. Upon introduction, the $110,800 SL550 is equipped with a standard 4.7L, 8-cylinder, engine that achieves 17-mpg in the city and 25-mpg on the highway. an Automatic transmission is standard. The $86,950 Base is equipped with a standard 3.0L, 6-cylinder, engine that achieves 20-mpg in the city and 28-mpg on the highway. an Automatic transmission is standard.