An alternative to renting a car is car sharing. Unless you wish to rent a car for a longer period, you might consider the use of some car sharing companies to get you from and to Prague Airport. With car sharing vehicles, you can park the car anywhere in Prague in the blue zone for free. Rental cars can be rented for minutes and up to seven days as needed. No worries about parking fees, insurance, fuel, servicing or cleaning.
CAR4WAY car-sharing has vehicles at the airport and you can sort out everything online before you arrive. All you have to do is to register on their website.