That's the best price we could find for select routes by at least $9. Buy Now at DealBase Tips On the DealBase landing page, click "United Airlines" in the top line to see this sale. We found this price on flights departing from Boston, MA (IAD) with arrival in Washington, D.C. (IAD) on February 4. Book this travel deal by January 21 for travel through May 20. All prices, dates, and booking details were valid at the time of publication.