Car rentals from both Enterprise and Avis are available right here at the airport. Reservations should be made in advance through the national reservations services for each agency.
Further information is available from each on site flight services office as well:
Emerson Aviation: 603-293-7980 or toll-free 800-808-2687
SkyBright: 603-528-6818 or toll-free 800-639-6012