This is the approach we took several years ago and it saved us a lot of $$$.
1.Don't rent at the airport (PHX)!. Choose an off site car rental agency.
Enterprise can be very cheap, away from the airport.
2. Search online for an Enterprise coupon code (e.g.
http://www.carrentalsavers.com/enterprise.html) These are not necessarily the best or cheapest ones for you. Do a thorough search and see what else you can find.
3. If you are arriving by air, consider staying the first night at a motel near the airport with a free shuttle.
4. Take the (free) shuttle to the hotel/motel, spend the night there and have Enterprise pick you up there the next morning. They will do this for you free of charge. Of course, your reservation must be with a branch location that is closest to your hotel/motel. This is the Enterprise location we used:
1131 W BROADWAY RD
TEMPE, AZ 85282-1225
Tel.: (480) 829-3970
5. Alternatively, if you don't want to spend the night in a hotel/motel, then take a taxi to the off-site Enterprise branch.
6. At the conclusion of your rental period, repeat the same process without the additional one night's hotel/motel stay. Better yet, you may be able to persuade your Enterprise driver to drop you off at the airport itself. We did! (While off-site car rental branches can't pick up at the airport, they can and do drop off if asked discretely.)