Please advise on how to go to Ole-London Hostel in Macau from HKIA at the cheapest way.

You should first take ferry from HKIA to Macao, and then take bus from the ferry terminal to your hotel.
It is suggested to take ferry operated by TURBOJET from Sky Pier to Outer Harbour Ferry Terminal. 6 ferries are available from 12:00 to 21:30. The ticket fare is 254HKD for ordinary seat for adult.
After arrival, you can take bus no. 10 or 10A from the ferry terminal to Praça de Ponte e Horta. And then walk to the northeast for about 180 yards to reach the hotel.