If you are a graduate of a U.S. college or university, check to see if your alma mater has a contract rate with Avis, Hertz, etc., and if so, whether alumni are permitted to use the contract's "leisure" rate for personal rentals.

Using my alma mater's contract leisure rate for a five-day rental picking up in Boston city, but returning to BOS airport, I'm getting base rates of $230 from Hertz, and $245 from Avis.

If you have no luck with an alma mater rate, compare the AARP rate at Avis/Budget with the other rates you are finding. Even if you are under 50, you can still join AARP as an "Associate Member" for $20/year and enjoy member benefits.

Edited to add: University contract rates are not the same as alumni association rates; the latter are often worse than the former.