Olympic Air, Ellinair and Ryanair fly from Thessaloniki Airport (SKG) to Athens hourly. Alternatively, Simeonidis Tours operates a train from Thessaloniki Airport (SKG) to Athens every 3 hours. Tickets cost $15 - $23 and the journey takes 45 min. Greek Railways (OSE) also services this route 4 times a day.
From Thessaloniki airport fly to Athens airport then subway to Athens. 1 h 52 min $51. From Thessaloniki Flughafen bus to Thessaloniki Büro Simeonidis, walk to Thessaloniki, then train to Athens. 7 h 1 min $59. From Thessaloniki Flughafen bus to Thessaloniki Büro Simeonidis, walk to Thessaloniki Monastiriou, then bus to Athens Karaiskaki sq. 7 h 48 min $67. From Thessaloniki Airport (SKG) drive to Athens. 5 h 15 min $94.