I was recently on holiday in Portugal with my wife. On our way home we got a taxi from the hotel to the local train station, a 90 minute train to the town with the airport and then a 15 minute bus to the airport. All that combined was cheaper than the shuttle bus from Glasgow airport to Glasgow city centre. The 4.5 hour flight from Faro to Glasgow was also around the same price as the 4.5 hour buses from Glasgow airport to Inverness.