There is an ATM/exchange in the airport. Istanbul has been one of our favorite ports. We had an incredible guide - I think I posted it here under guides. A friend of ours found him. We were off put on initially meeting him wondering why he hailed taxis for us but it worked perfectly and he paid for them. Make sure you ask ahead of getting in them what the fare will be. It was cheaper for the guide to take us in a taxi than for him to park and drive. And parking is a huge issue.

The guide we used was via Levant - but it was not Levant. http://leventsolmaz.com/meet-levent-solmaz/