The 2005 Mercury Grand Marquis is available as a 4-door, 5-seat sedan. Starting at $24,585, the 2005 Mercury Grand Marquis GS (100A) is powered by a 4.6L , 8 -cylinder engine mated to an automatic transmission that returns an EPA estimated 18-mpg in the city and 25-mpg on the highway. The top of the line 2005MercuryGrand MarquisLSE (220A) , priced at $ 30,640 , is powered by a 4.6L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 18-mpg in the city and 25-mpg on the highway.