We will be staying at a convent outside of town. City bus stop at our front gate. Should we take a taxi cab or try a form of public transit?
A taxi from the train station to the airport costs 20 Euros. From your lodgings, expect to pay more (let's say 30 Euros, although you don't say how far out of town you'll be staying). The airport bus from the train station costs 5 Euros. The city bus to get to the train station costs 1.20 Euros,. Consequently, if you crunch the numbers, you'll see that a taxi will cost you more. The airport bus runs every 30 minutes, and gets to the airport in little more time than a taxi. If your flight does not leave in the early morning, and if you don't have too much luggage, using public transportation might work pretty well.