The 2003 Mercury Grand Marquis is available as a 4-door, 5-seat sedan. Starting at $23,970, the 2003 Mercury Grand Marquis GS (100C) 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 2003MercuryGrand MarquisLS Ultimate (230A) , priced at $ 30,170 , 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.