One more thing to think about: I know most Avis rentals charge a mileage fee, but I'm not sure about Hertz. I presume you included that in your calculations?

If both have mileage fees and you're driving directly from SFO-LAX in one day or two, it might be easiest to get a car SFO-LAX and a second "local" in LAX. Also, depending when your drive is within your 2 week period, it might be cheaper to get an SFO local car, an SFO-LAX car and an LAX local car so you only pay the mileage for the direct trip, instead of 40 cents per mile for the whole 2 weeks of touring around.

Good luck & enjoy the trip!