Per the link below, you can get round trip air on Turkish Air for a shade over $500 round trip. This is only from certain cities so you may not be able to find prices that low. You will probably have to connect in Istanbul. Good luck!
http://thepointsguy.com/2016/01/nyc-la-to-europe-from-508-round-trip/
Used Turkish Air and paid ~ $570 for one trip and $763 for another (round-trip). Had to connect through Istanbul both times and enjoyed the layover. Great airline, good food and service on board...would definitely fly them again because they fly a red-eye direct from one of my airports which makes it easy to sleep.
