The 2006 BMW Z4 is available as a 2-door, 2-seat convertible. Starting at $35,600, the 2006 BMW Z4 3.0i Roadster is powered by a 3.0L , 6 -cylinder engine mated to a manual transmission that returns an EPA estimated 20-mpg in the city and 30-mpg on the highway. The top of the line 2006BMWZ4Coupe , priced at $ 40,100 , is powered by a 3.0L , 6 - cylinder engine mated to a manual transmission that returns an EPA estimated 20-mpg in the city and 30-mpg on the highway.