There is a simple way to avoid the bulk of airport fees and taxes, particularly on longer term rentals. But as usual with my 'tricks' you have to be flexible, determined, and have all your ducks lined up.

You book two reservations -- one at the airport, for 1 day in the cheapest car you can find. You pay the minimalist fees and taxes, then promply drive it downtown (or to your hotel, to continue downtown the next morning) and drop it there. (Drop fees are almost never charged for these rentals, but check first.)

The second reservation is made for the duration of the intended rental, from the downtown location, and returned to the airport. It doesn't even have to be from the same company.

You avoid a lot of the fees and taxes, and sometimes the downtown locations will offer much better rates. At some of the more notorious airports (BOS for example) this can save hundreds of dollars over the course of a few weeks.

I know some people will say it takes too much time. Of late I've observed that these people often also say time is money. In this case, money is time.