There are lots of language programs that I’ve found in D.C., but for my money, the Graduate School above L’Enfant Plaza metro station offers several classes that provided a helpful introduction to my language of choice. The schedule, quality of instruction and class size worked for me and the price was roughly $350. You can find more about it here: http://graduateschool.edu/
There is also a language program at GW, but anecdotally, my friends have reported unpredictably mixed results there. It is much cheaper ($110, I think, for initial payment) and enrollment is extremely competitive. That said, it seems to support the notion that you get what you pay for.
Clearly, there are more expensive and higher quality classes (Berlitz, etc.), as well as other programs I haven’t listed. You may also have luck with your language and find conversation groups. There are some Meet-up groups that may work for your purposes, including DC Language Lovers. Good luck!