In May, the four of us traveled from the airport to Sultan Hill. We booked a Mercedes Vito minibus through the GetTransfer website. We paid 70 dollars, and the driver, Ahmet, spoke excellent English and even gave us a short tour along the way. He made a special stop at the Blue Mosque so we could get our bearings. By the way, here is the website https://gettransfer.com/en/directions/turkey/istanbul/airports/sabiha-gokcen where I booked the transfer. You can choose the class of car yourself and check the prices. And here's another tip from me: if you arrive in the morning, ask the driver to take the Galip Bridge there's almost no traffic, and the view is amazing! Are you staying for a long time? We were there for almost 5 days, and it wasn't enough.