Berlin has two airports, Berlin-Tegel and Berlin-Schönefeld.
Most flights will land at Berlin-Tegel. The journey by taxi from this airport to the centre of Berlin should take around 20 minutes and cost between €20 and €30.
The same journey by public transport also takes about 20 minutes.
The taxi journey from Berlin-Schönefeld will cost around €60 and last between 30 and 45 minutes, roughly the same time as the equivalent trip by public transport.