Through Burgas there are several buses a day. Perhaps the most convenient option - leaving at midnight, arrival in Istanbul at about 6 am. The buses themselves are very comfortable, the road is beautiful. Tickets can be bought in Bourgas at the bus station, which is next to the railway station, the price is about 60 leva (~ € 31). More details - on the official website of the bus station of Bulgaria www.centralnaavtogara.bg.

Other options - only with a transfer. For example, to get to Sofia (about 6 hours by train or bus, the price of the issue is from € 10 to € 40), and from there fly to Istanbul (1 hour 25 minutes flight, the price is about € 100).