The 2010 Mercury Grand Marquis is available as a 4-door, 5-seat sedan. Starting at $29,810, the 2010 Mercury Grand Marquis Base is powered by a 4.6L , 8 -cylinder engine mated to an automatic transmission that returns an EPA estimated 16-mpg in the city and 24-mpg on the highway. The top of the line 2010MercuryGrand MarquisFleet (100A) , priced at $ 29,525 , is powered by a 4.6L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 16-mpg in the city and 24-mpg on the highway.