Lufthansa has round-trip flights from Austin (AUS) to Istanbul (IST) for $703 with a connection. Flights November to March.
Fare is Regular Economy. Not Basic. Carry-on, checked bag, and seat selection are included without an additional fee.
Note: Some small OTAs on Skyscanner have this for about $684. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.