I've always used carhire3000.com, which I think is now rentalcars.com, but carhire3000 will get you there. Some interstate rentals have no one way fees, Nevada, Arizona and California for example, and if you rent within the same state, you may not have to pay drop-offs. We rented from Denver to Tucson last month and paid $300, easier than going back to Denver! It goes on distance between the two points, not mileage driven, I think the $300 is up to 1000 miles with Dollar.