United Airlines [united.com]
has roundtrip fares from Boston, Washington DC, New York and Chicago to Istanbul, Turkey for an average of $500 per person, roundtrip, including taxes. Fare valid (at the time of posting) for Wednesday departures and Tuesday returns so please be advised.
Searching a 6-day range, I see they're available over Thanksgiving. However, they are not available 2nd week of Dec through 3rd week of Jan 2017 for the holidays.
Sample date: Wed, Nov 23 - Tue, Nov 29, 2016
BOS-IST - $498
IAD-IST - $502
JFK-IST - $514
ORD-IST - $505
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