Depends what you want to do. If you plan to stay in Luz all the time and just take a short daytime bus trip to Lagos, a transfer will do you fine.
A return transfer to Luz from Faro Airport will cost, based on current prices, in the order of € 140.00 depending on the transfer company.
In October, you may be able to get a budget small Class A hire car for +- € 150.00 for a week which would allow you also to explore the Western Algarve.
