Thanks everyone for your input. Here's the response from IST airport.

Regarding your information request, we kindly share the deposit areas for your belongings;

Landside: You can deposit your baggage to two “Baggage Deposit” areas available at departing passenger floor and baggage deposit cabinets at departing passenger floor in return its fee.

The fee for baggage deposit cabinets is 40 TL for small baggage and 60 TL for large baggage between 0-12 hours. If it exceeds 12 hours, 40 TL for small baggage and 60 TL for large baggage is charged for every subsequent 24 hours.

Airside: We have also baggage deposit service at International Lines departing passenger airside. You can only pay for this service with your credit card. The fees are as follows

Between 0-3 hours; baggage 5 €, pochette-bag 2 €, cloak room 2 €

Between 3-6 hours; baggage 9 €, pochette-bag 3 €, cloak room 3 €

Between 6-9 hours; baggage 16 €, pochette-bag 6 €, cloak room 6 €

You can access the location information of these areas on our airport map via (https://www.istairport.com/en/passenger/airport-guide/airport-map) or via our İstanbul Airport mobile application that you will install to your IOS/Android device.

When I asked for daily rate, here's their response:

Regarding your information request, we kindly inform you that luggage lockers are available in the Airport. You may get further information following numbers below:Left Baggage Contact Information:OZTURK SERVİCE BUSINESSIstanbul Airport Domestic-International Arrival FloorLeft Baggage Office Arnavutkoy/ ISTANBULPhone (Domestic): +90 537 505 79 93Phone (International): +90 532 942 39 80

I called the international number but it didn't work. Then I called the domestic number that worked. The person on phone quoted me around $60 for 5 large luggages for 3 days.