An alternative to renting a car is car sharing. Unless you wish to rent a car for a longer period, you might consider using some car-sharing companies to get you from and to Prague Airport. You can park your car anywhere in Prague in the blue zone for free with car-sharing vehicles. 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.