Originally Posted by
berlindave
You could bike it in 4 hours. You will be one hundred percent fine. Cab it (probably 40-ish make sure he takes the A110/100) or take the 109 bus to Zoologischer Garten then to Hauptbahnof and then the Airport express (two changes, boring and annoying) suggest cab.....
I agree that a taxi is probably the most convenient option but mytaxi says it is rather ~50 EUR and tip and it may be 60. The bus+trains takes approximately 1 hour including changes and it can be done with one stop (TXL bus to main train station + airport shuttle to SXF).
As mentioned by berlindave 4 hours is absolutely doable.