Driving to Glasgow airport (international) GLA and back - Starting from Glasgow city centre

Driving from Glasgow City centre to Glasgow airport (GLA) dropoff/pickup. Currently driving through the dropoff costs £4 (you can wait max 10 min), and the longer you stay waiting in the area the higher the charge, £15 for 30 min waiting in case of pickup. I guess there is only one airport in Glasgow and that's the GLA (Glasgow Airport), which has most international flights. There are buses that go between GLA and the city centre quite regularly. There is also the PIK (Prestwick International Airport) which for some reason also widely referred to as Glasgow Prestwick Airport, which is not even in Glasgow, it's about 45-60 min from Glasgow city centre, and it's in Prestwick near Ayr. Usually for domestic and short-distance-international flights. I guess the best thing about PIK is that it has its own train station that connects it to Glasgow city centre.