Hertz has been offering some promotions on monthly or longer rentals. As mentioned, rent from a local rather than an airport location if you want to save on the taxes.

As part of a year-long RTW trip back in 2002 I rented a car in Vancouver and drove: Vancouver - Toronto - Chicago - Nashville - Pensacola - Houston - Dallas - El Paso - Salt Lake City - Spokane - Seattle - Vancouver over a period of about 14 weeks. Had a blast!