To come to Bukit Lawang or to leave it, there is two possibilities : private car or local bus.
The air-conditionned private car pick you up at the airport or in your hotel in Medan and bring you directly to Bukit Lawang. From Medan airport, it takes around 4 hours, from Medan city it will be around 3 hours.
From Kuala Namu Airport to Bukit Lawang (around 4 hours): Rp. 600 000
From Medan city to Bukit Lawang (around 3 hours) : Rp. 550 000
Drop off/pick up to/from hotel/airport in Medan/Bukit Lawang, stop at ATM and/or Money Changer
Public bus are leaving from the airport with a stop in Medan or Binjai. It takes around 5 to 6 hours to arrive to Bukit Lawang.
The fare from the airport to Binjai is 30,000rp by ALS (Antar Lintas Sumatera) bus. To get from the bus station to Bukit Lawang itself you can walk or take becak for 2 persons max (Rp. 5000 per person).
When the becak drops you off in Bukit Lawang itself, you will have a walk of 2 to 30 minutes to reach your guesthouse, depending on where you are staying.