Unfortunately Alaska is notorious for high car prices in the summer. If you could visit before May 31 you'd find cheaper rates but aside from the coupon codes you'll find in other threads in the various car rental forums, there's probably not much you could do. Even checking hotwire shows that there are no real deals to be had. You might want to try one of the smaller car rental places like Alaskacarandvan.com. They at least save on the airport fees and give you the 7th day free. Enjoy your trip to AK!