Sorry for the delay in reply!
I was on a rush trip to Lisbon and Seville.
You do not say where you are flying from Lisbon to.
Easyjet have flights from Lisbon on Saturdays to
London Gatwick
London Luton
Madeira
Milan
Paris CDG.
I will therefore only be able to give you generalised advice.
Firstly, very few direct long-distance coaches go directly to Lisbon Airport.
You will probably need to get to Lisbon Sete Rios Bus Station and then to the Airport.
There are Rede Expressos http://www.rede-expressos.pt/ buses from Cernache Bonjardiim to Lisbon Sete Rios as follows:
CERNACHE BONJARDIM LISBOA (174 Kms)
Depart Arrival Price Frequency
09:15 12:00 11.00 Daily Except Sundays and Mondays if public holiday
15:45 18:30 11.00 Sundays and Mondays if public holiday
19:45 22:30 11.00 Daily
For buses from Lisbon Sete Rios to the Airport see the following post on my blog:
http://barlaventostravelblog.blogspot.com/2008/12/lisbon-airport-buses-to-centre.html
