Thanks, as far as keeping within your budget, do you have an idea of what you are willing to spend on a vacation each year? Or do you just spend accordingly with where you want to go?
I try to keep to a budget within every place I visit. However, I always bring more than enough funds in case I decide to spend more or for unexpected expenses.
My advice is to take vacations during the fall/spring to save money and avoid crowds. This way you're not vacationing when school is out for the summer or during the winter holidays. There's usually a decent amount of daylight during the fall/spring as well.
If you really want to save money, stay in hostels. There're usually $30-40 a night and are great for solo travelers.
I agree with other posters that D.C. sure won't be a relaxing vacation. When I was there for 3 days, I saw a lot of sights during the day and partied at night. Lots of walking. Probably only slept 12 hours that whole time.
Oh and get used to paying $10 per drink.
Hope this helps.