Istanbul is the main city for international arrival/departures. There are two airports in Istanbul ( Ataturk Airport is situated in the European peninsula and Sabiha Gokcen Airport is situated in Anatolian ( Asian peninsula) .
Turkey is serviced by several international and regional budget airlines. Also there are rent-a-car services ( international brands/ local brands) at the airports and also in the city.
The train is also an optional way of transport.
The taxis are cheap compared to many European cities. There are also national coach bus services that are available 24/7.