This is a very difficult question as everyone has their own lifestyle and spending limits.
As a rule of thumb, you should have enough money to survive at least 90-120 days if you’re coming to Turkey without a job offer.
If you have a job offer/contract, then two month’s spending money plus rent deposit should be enough until you get paid.
Between $2000 t0 $3000 should be about enough for you to survive until you get your first pay. You’ll need to pay a deposit to your landlord for the apartment. You might need to pay deposit to have the electricity and water turned on. You’ll probably need money to get internet setup and a local SIM card.
Eating is not expensive in Turkey. You can eat for as low as 15-20 TL for lunch or dinner. Transport cards can be topped at 200 TL with unlimited travel on bus/train/ferry/tram.
Rest deposits depend on the apartment and your monthly rent depends on the location. We always advise teachers to choose a location close to the school where they will be working. Traffic is INSANE in Istanbul and it’s not worth spending a total of 3-4 hours commuting. It’ll drain you of the energy that you need to work.
It is not difficult to find a roommate if you do not want to bear the burden of rent alone. There are many websites where you can search for roommates, but we recommend sharing with a fellow teacher or someone professional.
Be ready to spend approximately 2500 TL per month if you plan on staying on your own and roughly around 1500 TL per month if you resort to sharing the apartment with a roommate. The estimates include all utilities, but it could vary depending on the area.
Favorites and central spots for foreigners are Kadikoy, Taksim, Sisli/Mecidekoy, Levent and Besiktas. The transportation system is excellent in Istanbul - as long as you factor in the wait and transfer time.
Clothing and apparel are relatively cheap. There are many malls with the usual shops and some quality Turkish labels, too. Most foreign food brands are available in Istanbul and if you can’t find what you are looking for, then be sure to visit the grocery store called Macro Center. They even carry my favorite Reese’s Peanut Butter Cups and Chips Ahoy chocolate chip cookies!