The 2004 Mercury Grand Marquis is available as a 4-door, 5-seat sedan. Starting at $24,370, the 2004 Mercury Grand Marquis GS (100B) is powered by a 4.6L , 8 -cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 25-mpg on the highway. The top of the line 2004MercuryGrand MarquisLS Ultimate (230A) , priced at $ 30,725 , is powered by a 4.6L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 25-mpg on the highway.