This is a $100 price drop!
ANA / United Airlines have round trip airfares travelling from Washington DC (IAD) to Ho Chi Minh City Vietnam (SGN) for $571, making one stop in Tokyo.
Departs IAD: Aug 26 thru Nov 30, almost daily
Returns: wide and good availability
Use dates and book it directly with United Airlines . It’s only $10 more on Expedia if you rather use Expedia
http://www.united.com/