Not bad for a last minute trip to Turkey! Fly from DC to Istanbul for $399 round-trip, nonstop, including all taxes, on Turkish Airlines.
We found dates available for travel as soon as next week, returning the following week. Seems to be pretty scarce, for early to mid-March, with fares varying slightly by date.
Lots of other great fares to Istanbul, as has been the case for a good while now. For a complete list of current findings, see our Istanbul page.