Greyhound services Ocean City. They leave from the West OC park and ride lot and go to New Carrollton, MD. From New Carrollton you can take the MARC Train to BWI or take a combination of the Metro Orange Line and a taxi to get to Dulles. For more information on Greyhound times call 800.231.2222 or go to
https://www.greyhound.com/farefinder/step1.aspx . There is one bus a day from OC to New Carrollton that leaves OC at11:05am and arrives in New Carrollton at4:50pm. It costs between $40 and $60 depending how far in advance you reserve a seat and the options you select.
Another option is the Bay Runner Shuttle which runs from OC to BWI. It is about $100 and runs frequently. More information on
Bay Runner Shuttles can be found at
http://www.bayrunners.com/ You can also fly from Salisbury airport to a few airports. They used to fly to BWI and Philadelphia from Salisbury.