The problem with the luggage lockers in the CIP lounge is that a. there aren't enough and there are often none available and b. lots of them have broken locks, When you exit the customs are into the main arrival/meet and greet area, turn right. Next to the TK hotel desk is a left luggage operation. I believe it's open 24 hours. I left a bag there for 24 hours and I think it cost just 20 TRY.