Our cars are older, so we often rent a car for longer trips.
When I have to rent a car, I visit Hotwire and Expedia to get a ballpark range of prices. I like that Hotwire shows the entire bill, taxes and fees included, before you buy.
Then I go to Priceline and bid at least three dollars a day cheaper than the lowest Hotwire fare. If I have time, I bid much lower and then re-bid in the coming weeks. Otherwise, I stay in the three-dollar-lower range.
Five out of five times, I have had a successful bid. Even our contacts in the car rental industry have been surprised at the good rates we've gotten at their own company!
Priceline saves me money in more than rental rates: their surcharges are somehow less. All these fees are clouded in mystery, so I can't offer an explanation.
All I know is that I usually pay $20 less than the quoted fees and surcharges at Hotwire.
On this trip, I saved over $60 by choosing Priceline over Hotwire. I also think you are more protected from crazy return charges by paying up-front through Priceline than having an "open account" when you rent at the desk.
Last trip I returned the car a day early, for which Avis would have charged me a fee had I not pre-paid the tab through Priceline.
Don't forget to call your car insurance before leaving home and checking your policy for a rental car rider. Mine includes 14 days of rental insurance in my regular coverage. That way you can decline the pricey rental policies with confidence!
It goes without saying that public transportation, free hotel shuttles to the airport, and walking are all more frugal ways to get about on vacation. I hope the strategies above will help you when those choices are unavailable.