I've looked at all the links RickSteves has posted for cheap flights. Anyone have any other ideas beyond Turkish Air, Tarom, and Pegasus? I'm going in June. Thanks!
If Pegasus is not affordable for you, then you do not have any option to find cheaper 'direct' flights.
If you can handle 17 hours , take train from Istanbul to Bucharest with 4 hours connection time in Sofia Bulgaria.
38 Euros.Departures at 22:00 from Istanbul daily.
The train also includes a 3:00 a.m. border check at Kapikule, just for fun.