At Sabiha Gökçen Airport, many people overlook an important detail: deposit-free car rentals are available at the pick-up counter inside the terminal, not in the outside parking lots. Several companies offer car hire at Istanbul, typically at the airport, and their terms and conditions vary greatly. For example, various options are listed here
https://turkey-rentcar.ru/en/airport/sabiha-gokcen/ Comparing prices before arrival can save you real money, sometimes up to 30% or more off the total cost.