Both ways it is free of charge irrespective of airlines & nationalities. They don't check your airline tickets, nothing at all.
Frequency of busses every thirty minutes during peak hours 7am-8pm thereabouts, & hourly for early & late hours(5am - midnight?),and adequate seatings for appprox. 20 passengers.
I have observed some latecomers seated on the floor with their luggages.
Trip time can be as quick as 60 minutes as busses take the expressway.