Sammy Lee at Capitol Hill Tailor Shop was fantastic. I also took a bridesmaid dress here and to fix the hem on a chiffon dress and take off a strap, it was $60. Others on Yelp have complained that he was expensive but I felt it was reasonable given the material he was working with.
615 Pennsylvania Ave SE
(between S 6th St & S Seward Sq)
Washington, DC 20003
Neighborhood: Capitol Hill/Southeast