I was there this afternoon for a few hours, very enjoyable, amazing aircraft and history. Not too many people, entry is free, cab from IAD was $15 (10 minutes), I then took the center shuttle bus to the main location in the city, $7 round trip, I did not use return however, cab from Union station to IAD was $55, find yourself another way if you can, say Supershuttle. transit time was a little under an hour each way.