One way ERL ticket from KL Sentral to KLIA or KLIA2 is RM55.
To save RM31.80,
- Buy a one way ERL ticket from KL Sentral to Salak Tinggi for RM18.30 and board the train.
- Alight / exit from the train when you reach Salak Tinggi.
- Buy one way ERL ticket from Salak Tinggi to KLIA/KLIA2 for RM4.90.
- Board the next ERL that should arrive within 20 - 30 minutes.
The catch here is you will waste 20 - 30 minutes since you will stop at Salak Tinggi to buy ticket and board the next train. But if you are not in hurry, this is definitely cheaper (total cost: RM23.20) compared to the one way ticket from KL Sentral to airport (RM55.00).