best cheap DC eats
There is a good and reasonably priced brunch at Monroe's in the Del Ray neighorhood of Alexandria. It is also a great place for reasonably priced Italian food - and the $2 glasses of wine from the bottle left on the table - well, can't get much cheaper.
Check out 23rd St. in Crystal City - near both the Pentagon City and Crystal City metro stops - there is Taco House, which is great cheap Mexican, the Crystal City Sports Pub, a couple of Italian places you might like, and a good Vietnamese place - all reasonably priced.
Hope this helps.
For breakfast on the weekends, I like "Whitlow's on Wilson". It's about two blocks down Wilson from the Clarendon metro stop. (By "down", I mean towards Rosslyn.) Menu and other stuff is on their web site, below.
It's not accessible by metro, but the Cowboy Cafe on Lee Highway also does breakfasts on weekends. I haven't tried it, though, so I can't vouch for quality.
Bob & Edith's is not far from the Pentagon, but not readily accessible by metro. I won't mention much about it here, since there are whole threads about it.
Please feel free to e-mail me if I can give other breakfast recommendations--it's a favorite!
(Standard disclaimer: I am not affiliated with these restaurants in any way--except that I eat breakfast there frequently)