We're taking an RS Greece tour in April, 2019. Would like to spend a few days in Plovdiv, Bulgaria before the tour. Will probably fly Los Angeles to Istanbul on Turkish Airlines. Anyone know best way to get to Sofia, Bulgaria, then Sofia to Athens? Trains? Buses? Seems like flights from Sofia to Athens go through Istanbul, which seems a waste of time.
Google "Sofia Bulgaria to Athens flights" and you'll see three budget carriers with short, non-stop flights: Ryan Air, Wizz Air, and Aegean. Turkish Air flights connect through Istanbul because Istanbul is a huge hub; it makes sense for a national airline to use a main hub to fill more seats.
You can get to Plovdiv from Sofia and back via train or bus
http://www.visitplovdiv.com/en/how-to-get-to-plovdiv