ABC News' Becky Worley reports:
1. Check blind booking sites like Hotwire and Priceline.
They may not tell you who you're renting from but they will tell you what class of car you're looking at. And after all, a sedan is a sedan. The last booking I made this way, I saved $45 over the travel sites or directly from the rental company. The only downside is you have to prepay in full with penalties if you cancel. So this only makes sense of the trip is set in stone.
2. Use a price-tracking service.
If you do rent from a mainstream rental company, enter your trip details into Autoslash.com. It's a free tracking service that follows the fluctuating prices from the rental sites for your dates and alerts you if the prices goes down.
3. Try a car sharing service. They're now at the airport.
Zipcar has 14 airport locations in the U.S. with more rolling out all the time. These cost between $69 and $89 a day for existing Zipcar members and can be very competitive because it also includes gas, insurance and tolls. Also, Zipcar has found a niche renting to the 21 to 25 age group - people who are usually charged exorbitant fees by traditional rental companies, so this option makes a lot of sense for them and for anyone who regularly travels to the airports serviced by Zipcar.
4. Rent outside of the airport.
On average, renting at the airport adds 10 percent to your overall rental fee, and 20 percent in Europe. So if you can, get a shuttle to your hotel and rent remotely. Also some rental companies - such as Enterprise - will come pick you up within certain distances to their offices. So if the cost of a shuttle is minimal, the rental savings could be significant.
5. Use the sharing economy.
Relayrides.com lets you rent directly from a car owner. It's like VRBO for cars. I priced SUVs in San Diego and Jason's SUV was $120 cheaper than the lowest priced SUV I could find on Orbitz.com. Granted, you take the risk of an unreliable car owner or a dirty car, but reviews from previous rentals all claimed Jason was prompt in delivering the car and kept a very tidy Honda CRV.
Flightcar.com is trying a different tack on the direct rental idea. People parking at the airport rent their vehicle out to other travelers. If you're the car owner, not only do you avoid parking fees, you can make up to $20 a day. The service is still in early days - with only two airports and limited membership, but I can imagine a day when paying to park at the airport is purely optional.