Return flight Gatwick to Lisbon - depart Monday 18th September OR Tuesday 19th September / return Thursday 28th September - £55.72 @ easyJet

Thank you pikachu545

Those are mostly 10-15 min rides. 2 rides at sintra between the castles 6 euros each and sintra train station to Lisbon roma station at 18.20 euros. Lisbon card can be handy as well- it is about 24 euro for 24h but you can use it on public transport (including yellow tram) and trains to sintra + it gives free (and sometime que jump - e.g. Geronimo monastery) to some tourist sites. We had it for 24 hours (48h version is also available) - and used to go from Lisbon to sintra. It has expired and on the way back we took a taxi.
Also, when you enter your destination in google maps - you can see different options of how to get there - walking, public transport and using Bolt with an estimate cost.