Cafe Asia, with locations downtown and in Rosslyn, Va., has the cheapest quality sushi I’ve found in the D.C. area.
Try their happy hour Monday through Saturday, from 4:30-7:30 p.m. for $1 Nigiri sushi and $2 select draft beers. Get there as early as possible because in my experience (I’ve only been to the Rosslyn location) lines get pretty heavy after 5 p.m. because of the work crowd.
Non-happy hour menus are relatively cheap at Cafe Asia too. They’ve got a reasonable selection of delicious and unique salads that are huge; definately enough for a meal.