The only transportation at the airport are buses that service the carparks and between the domestic and international terminals (as they are around a 5 minute drive apart!). No trains come anywhere close, unfortunately. The buses are free from the carparks to the terminals (at the international terminal, one of the long term carparks doubles as the staff carpark, and staff have to be bused to the terminal with regular passengers). I'm unsure if the inter-terminal bus is free or not, and thus am not sure if airline staff get discounts or free tickets.