Lisbon International Airport is 90 km away from Peniche. By car, using the A8 highway, it will take you about 1h15 to get there. The road has tolls, so be sure you have cash to pay. You can book a car from one of the several rental companies at the airport.
An other cheaper option is to catch on of the few express buses. There are a few each day connecting Lisbon to Peniche, departing from the Campo Grande terminal by the Sporting Lisbon stadium.
You will sometimes find some cheaper fares if you fly to Porto (2h30) or Faro (3h15), especially if you are already somewhere else in Europe, but then keep in mind that your trip to Peniche will be longer and more tiring.
