I rent a lot of cars for work, although not in NH, but that seems high to me for a 7+ day rental.
Costco travel often has better rates than directly though the rental company. If its feasible to rent away from the airport (i.e. friend or public transit to a non-airport location) the rate can be much lower. I've had instances where renting from an off-airport location (but within 10 miles of the airport) cut the rental cost by 50-70%. If I'm not using Costco, I get to the rental site through Ebates.com, which gets you a percentage back after the fact. Good luck.