The 2008 Mercury Grand Marquis is available as a 4-door, 5-seat sedan. Starting at $25,435, the 2008 Mercury Grand Marquis GS (100B) is powered by a 4.6L , 8 -cylinder engine mated to an automatic transmission that returns an EPA estimated 15-mpg in the city and 23-mpg on the highway. The top of the line 2008MercuryGrand MarquisLS (200B) , priced at $ 28,325 , is powered by a 4.6L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 15-mpg in the city and 23-mpg on the highway.