Parking at the airport is free if you use the airport's dedicated car-sharing parking. However, you will be charged an airport fee whenever you start or end your trip at the airport. These fees are often determined together with each airport. Here is the full overview of all airport fees:
Austria
Vienna International Airport (VIE) – 11,99 €
Denmark
Copenhagen Airport, Kastrup (CPH) – 50,00 kr.
Germany
Berlin Brandenburg Airport (BER) – 7,99 € (available as of Nov 1st, 2020)
Berlin Tegel Airport (TXL) – 5,99 € (no longer available as of Oct 31st, 2020)
Berlin Schönefeld Airport (SXF) – 5,99 € (BER Terminal 5)
Düsseldorf International Airport (DUS) – 5,99 €
Frankfurt Airport (FRA) – 6,99 €
Hamburg Airport (HAM) – 6,99 €
Cologne-Bonn Airport (CGN) – 5,99 €
Munich Airport (MUC) – 13,99 €
Stuttgart Airport (STR) – 5,99 €
Italy
Milan Linate Airport (LIN) – 5,99 €
Turin Airport (TRN) – 5,99 €
Rome Fiumicino Airport (FCO) – 9,99 €
Rome Ciampino Airport (CIA) – 5,99 €
Netherlands
Amsterdam Schiphol Airport (AMS) – 8,99 €
Hungary
Budapest Ferenc Liszt International Airport (BUD)
– 890,00 HUF for taking a car
– 1.590,00 HUF for leaving a car at the airport