Originally Posted by Mr. July
Take the IAD express bus. I don't think there's another local bus option - but if there is, it's not worth the time and because it may involve multiple carriers (Metro, northern Virginia providers) it could end up being as expensive.
Other than that, I think your hotel stays will allow you to take the metrorail (unless you go to Baltimore, and that's discussed above), so rely on single fares - although you should buy one farecard with all of the money you think you'll need for the trips versus buying a new farecard each time - or, maybe, a rail-only pass if you think that's going to be a better value (the likely answer is no).
I understand your advice. My rough calculation is:
Metro Bus
Day 1: IAD-Hotel ~4.50 $ ~3.00 $
Day 2: Hotel switch ~ 2.50 $ ~ 1.25 $
Day 3: Hotel switch ~ 2.50 $ ~ 1.25 $
Day 3: Visit to DC ~ 5.00 $ ~ 2.50 $
Day 4: Hotel switch ~ 2.50 $ ~ 1.25 $
Day 5: Hotel-IAD ~ 4.50 $ ~ 3.00 $
Total single fares: ~ 21.50 ~ 12.00 $
--> Metro with limited use comes to almost the same as bus pass 11 $/short trip pass 22.00 $
Hence, the best is probably really the single-bus-fare-thing and for the DC-visit-day to buy a one-day-metro-card for 6.50 $