Actually GoBE is no longer €25, they put the prices up recently.
They're now €17 single if booked online and €27 return. Walk up prices are €20 single or €30 return with 10 services a day in each direction. (mostly every two hours)
Aircoach are €15 single booked online and €25 return, with walk-up €18 single and €28 return with 17 services a day in each direction (mostly every hour)