Cheapest way to rent a car?

My friends and I are organizing a road trip from Phoenix, AZ to Vancouver, BC. Because it would be a one way trip, we need to rent a car. The problem is every car rental company doesn't let us pick up the car at Phoenix and drop it off at Vancouver. The only one that lets us do this is Hertz, but we think it's really expensive. Does anyone know a reliable car rental company that we could compare with Hertz? or does anyone have any suggestions at all??