We enjoyed Greenbelt Park with a daily camping fee of $16/day ,
but it is dry camping. This may have increased this year to $20/day. The camp ground has showers, dump station & water. It's
a 10 minute drive to the Collage Park Metro Station or a 30 minute walk partly
thru the park. We stayed 12 days and saw most of DC's attractions last fall. The US National Parks staff were very helpful, even suggested and directed us to the nearby location to get Senior SmarTrip® cards for reduced rates on the Metro and also providing a Metro routes map.
https://www.nps.gov/gree/index.htm
