Istanbul Airport is 50 kms to old city. This is 45--55 mins. driving distance depend on the daily traffic. Celal Sultan Hotel offers Limousine services with magnificent view of Marmara Sea along the road to the old city where the Hotel located.
Istanbul Airport Transfer One way 60 Euros, Both ways 110 Euros
Sabiha Gokcen Airport Transfer One way 70 Euros, Both ways 130 Euros