You are making a horrible choice buying a property in Turkey. Right now the Turkish government can't even decide if it wants foreigners to live in Turkey or kick them all out. Right now you would have to buy your property in an area that has less then 25% of foreigners. Even peoples homes who are worth over 75,000 USD got rejected for ikhemets.
You are talking about a country who changes its laws almost every quarter calendar on foreigners. Most people had to sell their properties in Turkey at a loss, and as a foreigner your expected to sell at a loss.
Could you live on 500 USD in Turkey a month? Yes. But it will be hard. Your biggest expense is going to be natural gas in the winter time. If your someone who does not smoke, who does not drink alcohol, and who stays away from all vices. You can live a simple life in Turkey for 500 USD a month.
But you will not live that life on 500 USD a month in Istanbul, or any other tourist area in Turkey. You will be living out in the country side of Turkey or living in smaller towns that are not well known and have no foreigners living in it or very few foreigners. Places where 99% of the population speaks no English.
I lived in Yalova which was better then Istanbul for prices, and also that people didn't try to scam you every single day. But you still run into scammers if you give them the chance like everywhere else. Don't expect to go anywhere in Turkey or the rest of the world and trust everyone you meet. Expect that everyone is trying to scam you.
In order to live on 500 USD a month you can not convert all your money to Turkish Liara. You will have to send your money monthly by services like moneygram or western union to keep up with the rate that the Turkish liara is falling.
To give you an example of why you need to do this: I stayed in Turkey for almost 2 years. The first year I was there if I converted 1 million dollars into Turkish Liara by the end of the year if I converted it back to USD(With spending no money from it) I would only get back 400 thousand USD from how much the Turkish Liara devalued and it has only gotten worse since then.
Turkey is no longer a stable country, and I would suggest either finding a more stable country or forget about ever buying a house in Turkey until they decide to stop being schizophrenic and have a stable history of treating foreigners with respect. Which they have never had this history ever.
If you want to try to find a very cheap apartment (100-200 USD) a month. You can do that. But every single person I have seen with exception of a few foreigners have all lost money on their apartments, and homes. Many of them are so desperate they were willing to sell them for a huge loss to get their money out of Turkey.