Its an easy daytrip and worth the effort. Day tours are easily booked through your hotel and a taxi for the day would also be no problem. When I did it 15years ago I just took the public bus from downtown Bogota.

If you take a taxi for the day I'd strongly suggest doing the cathedral in the morning and stopping on the way back for lunch at Andres Carne de Res in Chia -a Bogota institution and worth a trip in itself. http://www.andrescarnederes.com/