Or you could buy a new car. I would go with a smaller car because they have better gas mileage, which is essential in Europe given the price of gasoline there (you may even want to go for a diesel vehicle as diesel gives good better gas mileage and is cheaper than gasoline). Small cars will also give you a huge advantage when navigating narrow or busy streets, and they are a breeze to park just about anywhere. If you have ever parked a car in a large city in Europe, you know why this is particularly important.
Smaller cars can be really cheap in Europe. My mom just bought one last month, the base price was only 8,000 euros (That's the car she bought: http://www.renault.ch/fr/gamme-renau...uvelle-twingo/
). After adding all the options (including a/c, airbags, CD player, etc...), she ended up paying just about 10,500 euros. When you are done with your trip, just resell it and recoup most of your money. The reason why I'g go with a new car is because I would pay a bit more money to make sure I don't get into mechanical troubles during my journey which is more likely to happen with a used car than a new one.