The 2005 Pontiac Grand Prix is available as a 4-door, 5-seat sedan. Starting at $24,960, the 2005 Pontiac Grand Prix GT is powered by a 3.8L , 6 -cylinder engine mated to an automatic transmission that returns an EPA estimated 20-mpg in the city and 30-mpg on the highway. The top of the line 2005PontiacGrand PrixGXP , priced at $ 29,335 , is powered by a 5.3L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 18-mpg in the city and 27-mpg on the highway.