At around 40-50zł with a recommended company such as Sawa Taxi (tel. 22 644 44 44), a taxi ride to Wilanów is something of a false economy, taking more or less the same time as the bus to get there. If you prefer the comfort and privacy of your own car then also look for ELE taxis parked around the city, including outside the (A/B-4) main train station.