The airport runs a mini-van shuttle bus service which is very reliable and cheap. You can also arrange pickup for the return trip to the airport. Some of the taxi companies are honest, Fotaxi and Radiotaxi are 2 (there are others), and offer a special rate to the airport from parts of Pest that is competitive with the shuttle bus. The problem taxis are easily recognized (they are generally Mercedes Benz private cars with a removable sign on the roof, rates are 5x to 10x higher than a real taxi; but they speak english while most of the regular taxi drivers do not ... so have your destination address written out).