|Renting cars in France allows us to stop at lovely picnic spots like this one.|
While this is an opaque site (You do not know the company providing your service until you've paid, but you are told the star number or rating before you buy.), I've been using it for years and never been disappointed with the service. I always check to make sure Hotwire is giving me the cheapest price possible, and I always find it to be half to one-third the price I find on any other site.
Hotwire was started in 2000 by six airline companies anxious to sell their extra seats. It's expanded to offering hotel and vacation package reservations and car rentals. If you've never heard of them before, give them a try when you're doing your comparison shopping. I don't think you'll be disappointed.