The 2007 Chevrolet Impala is available as a 4-door, 5-seat sedan. Starting at $21,015, the 2007 Chevrolet Impala LS is powered by a 3.5L , 6 -cylinder engine mated to an automatic transmission that returns an EPA estimated 21-mpg in the city and 31-mpg on the highway. The top of the line 2007ChevroletImpalaPolice , priced at $ 23,670 , is powered by a 3.9L , 6 - cylinder engine mated to an automatic transmission that returns an EPA estimated 20-mpg in the city and 29-mpg on the highway.