Hyatt Centric Hotel, Levent,Istanbul
It is situated in Levent (on the European side) next to Levent metro station.
There is a shuttle service from Istanbul Airport to Levent. The shuttle number is “Ist 5”. Get off at Zincirlikuyu stop.
https://www.hyatt.com/en-US/hotel/turkey/hyatt-centric-levent-istanbul/istct
Single room 150 Euro
Double room 165 Euro
There are lots of other hotels to stay between Levent and Yenikapi. You can get to conference venue hotel via metro from anywhere in Istanbul.