There are over 1000 hospitals in Turkey under the Ministry of Health. Approximately, 100 in Istanbul. These numbers do not include clinics. When you have that much opportunity, competition arises. Therefore, our health system is fast, responsive and trustable.
There are lots of professors, doctors and medical staff who are highly educated. This is the first reason why hair transplant is cheaper in Turkey, because there are many choices.
The other reason is exchange rate. Turkish Lira is much cheaper than dollar, euro, pound and other currencies. And the other reason is accommodation choices. Istanbul is a big city with lots of houses and hotels. You may rent a house while your visit or stay in a hotel.