The best way to go to Boston MA from Washington DC is to take a bus from DC to New York City and a second one from NYC to Boston. The average cost of ticket from Washington DC to NYC is $20. ( one way) Departs are every hours from 7am to 1:30 am Average Duration: 4 hours.
The average cost of ticket from NYC to Boston MA is from $15 to $30 (one way) Departs, hourly, from 12.15am to 10.30pm, Average Duration: from 4 to 6 hours.
So for wahington DC to Boston Massachusetts in bus : Average cost: from $35 to $50 one way. Average duration : 8 to 10 hours
Only Greyhound provide a solution for $49 (web only fare) duration from 9h50 to 11h50 but you still have to 2 buses and stop at NYC
