How much would it cost using airport express from HK airport station to causeway bay mtr station?

For taking the mtr, you need to take the airport express to HK Station and the fare is around 100HKD per adult.
Then you need to walk to the Central Station to take the Island Line to Causeway Bay Station. For this part, it is no charged if you use the Octopus card and it is 5HKD if you buy the train ticket at the ticket office.