The closest airport is Faro which is just about an hour drive to Praia da Luz along the new motorway which extends from Faro to beyond Lagos. Faro is well served by scheduled and charter airlines, including BA, TAP, Easyjet, Monarch, BMI etc.
Alternatively flights can also be taken to Lisbon airport which is approximately 2 hours 30 mins drive away, again mainly on motorway. At peak holiday times, particularly if booking late, Lisbon can sometimes produce significantly cheaper flights.
To check out prices for the period that you are interested in just click on the airline name below to go to their website.
There are many more airlines and search sites, but this should give you a good idea on prices-CONTACT US if you want further help or advice on flights.