The taxi fare from downtown Bucharest to the airport (or the other way around) should be of around RON 50 (less than EUR 10), depending on traffic. Make sure to take a cab with a fare below RON 2 per km, you will see it written on its door. They might try to convince you to pay the trip back to the city but you should not do so, as they will get a customer back. When arriving, use the official cab ordering device, which is multilingual and which issues a ticket mentioning the cab company, cab number and time until arrival. Then wait for your cab in the area marked with two yelow flags outside the terminal.