If you're planning an extended stay in Europe - one lasting 17 days or more - it may be cheaper for you to temporarily buy a car and then sell it back at the end of the rental period.
Due to some anomalies in European tax laws, especially in France, car manufacturers end up scoring a tidy extra profit on reselling these "used" cars, so they're happy to make it easy for foreign travelers to use a brand-new car during their trip to Europe.
What's more, it may be the only way the very young (18 and over) or elderly can get a car to drive in Europe, as many car rental companies have age restrictions. These restrictions may require extra fees or may simply make it impossible to rent at all. There is no upper age limit on these buy-back deals; many car-rental companies start age restrictions at 70 and by 80, it's virtually impossible to rent a car.
Auto Europe and Peugeot have a collaboration going on right now which makes it even easier to sly-buy a rental car. While it's cheapest to start and end in France, for an extra fee you can get or drop off the car in a number of other European cities. There is normally a limit of 175 days - essentially six months - on how long you can keep the car, but exceptions can be arranged for students, teachers, "trainees" and missionaries.