The Herndon-Reston Holiday Inn Express is located close enough to Dulles Airport that they provide a complementary shuttle service to the hotel. In addition, this hotel is located close to the Weihle-Reston METRO station. The hotel shuttle will happily take guests from the hotel to the METRO and back. At the end of my trip, they happily picked me up at the METRO station and dropped me off at the airport. The shuttle also took me to and from church on Sunday morning. They also are happy to take any guest to any restaurant within a 3-mi radius.
It costs me about $120 for pay for 4 people to travel to DC and back to the Weihle-Reston station 3 times with a 4th short hop from Smithsonian to the Capital South station. Remember that it is more expensive to travel during weekday peak hours.
When you get to the Dulles Airport, make sure you don't just hop on any Holiday Inn shuttle. There are several Holiday Inn hotels in the area and they all pick up guests at the same curb spot 2H. The Holiday Inn Express uses a blue and white shuttle van while the regular Holiday Inn use larger green and white shuttle buses.