I go to One Life Capitol Hill at 3rd and G St SE. Worth checking out. Don't know if it's the best gym in Capitol Hill (and I doubt it's the cheapest) but it's worth investigating:
https://www.onelifefitness.com/gyms/capitol-hill
It is in what was once one of the first (or the first) public schools for kids freed from slavery. I wish it was still a school - but it does give you that feeling of an old fashioned gym. The school was named for JR Giddings, an anti-slavery Congressman from Ashtabula, Ohio, and the name is still on the building.