Agree with the above posts. You will almost certainly do better off-airport price-wise, but it is a bit of a roulette game selection wise.

One thing you might want to consider since you are landing at SFO is to initially rent a one-way rental at SFO to a local Hertz office near where you are saying. This could be any length rental that you choose (see what works out best price/convenience-wise). Then have a second rental scheduled to pick up at the local office at the same time you are returning there. You'll avoid all those egregious airport fees by renting off-airport, and you can even make that rental a one-way returning back to the airport for convenience.

Also, keep in mind that if you are relying on credit card insurance coverage for your rental, many of them max out at 30 days, so you'll want to check on this before you leave and possibly break up the rental into separate 30-day or fewer rentals anyway.

You can, of course, book and track your rentals with AutoSlash if you wish. This means that while you're driving around in rental #1 , AutoSlash can be checking for lower rates on the rentals you are picking up in the future. It very well may save you money, and you can apply your Hertz 5* member number when checking out and get all the same status you normally would when booking directly with Hertz.