Some colleges/universities (generally the larger, private ones) have rental-car contracts that alumni are entitled to make use of. So maybe contact your alma mater's Fiscal Affairs office and inquire if: 1) the school has any rental-car contracts, and if so; 2) whether alumni may utilize the contract's "leisure" discount code.

If there is no alumnus discount available to you, try requesting a quote from autoslash.com, which will monitor any reservation you make through them, and alert you if and when there is a better rate available from the same, or a different, rental company.

Yet another option (if you are under 50) is to join AARP as an "Associate Member," which will entitle you to special rates (and some insurance benefits) when using the AARP rate at Avis/Budget.

And, of course, always compare prices for an airport pick-up with prices for an off-airport pick-up.

Edited to add: xooz beat me to the punch re: autoslash.com.