The 2008 BMW Z4 is available as a 2-door, 2-seat convertible. Starting at $40,700, the 2008 BMW Z4 Coupe is powered by a 3.0L , 6 -cylinder engine mated to a manual transmission that returns an EPA estimated 18-mpg in the city and 28-mpg on the highway. The top of the line 2008BMWZ43.0i Roadster , priced at $ 36,700 , is powered by a 3.0L , 6 - cylinder engine mated to a manual transmission that returns an EPA estimated 18-mpg in the city and 28-mpg on the highway.