I just received an email that asking -- "I'd love to have your top 3 recommendations for meals under $10 in the city." I answered the email, and wanted to share my answers on here.
Eating for cheaper is becoming easier and easier as restaurants get faster and more casual, but ten dollars is still a low number, so I have restaurants where the meal would be no more than 12 not including beverages. My top three probably are --
Donburi (Adams Morgan, Japanese) This place is a narrow space with a counter and a small front for takeout. They serve both meat and fish (chicken, sushi tuna, salmon) over rice with other fresh ingredients. A sample dish of theirs is their "Oyakodon" which is a sous-vide cooked chicken thigh, caramelized onion, two eggs, scallion, and donburi sauce for $8.18.
Bub and Pop's (Just South of Dupont, Hot Sandwiches) This place serves gourmet Italian sandwiches, and it's name is always brought up when discussing best sandwiches in the city. It's a small space, so seats are hard to come by at lunch but later in the day seats are usually available. The sandwiches are huge, and are available as whole sandwiches ($15) or halves ($8.) There are tuna melts, hoagies, brisket, pork, and turkey and one or two vegetarian options.
Taqueria Nacional (14th Street Corridor, Tacos) Considered the best tacos in town by some (including me,) the tacos are $2.75-3.50 each and are big enough that eating three is good for a meal. The space is really cool, and it is a quick and cheap alternative to the more expensive sit-down restaurants that line 14th Street. A steak taco, a chicken taco, and a refried bean taco would come out to $9.75 before tax.
So that's my answer. But also who am I to tell you what the best cheap eats are in DC. Washingtonian's List of Best Cheap Eats is probably a better place to start than me. These three places are all the bomb though.