The 2008 Chevrolet Impala is available as a 4-door, 5-seat sedan. Starting at $25,330, the 2008 Chevrolet Impala 3.9L is powered by a 3.9L, 6-cylinder engine mated to an automatic transmission that returns an EPA estimated 18-mpg in the city and 28-mpg on the highway. The top of the line 2008 Chevrolet Impala Police, priced at $24,300, is powered by a 3.9L, 6-cylinder engine mated to an automatic transmission that returns an EPA estimated 18-mpg in the city and 28-mpg on the highway.