Trina:

Something else you might consider, if you can, is a one-way car rental from the Richmond area to IAD.

We looked into that a few months back when we were booking a vacation where it was cheaper to fly out of IAD than RIC, but the flight back was about the same. We looked into the major rental companies (but away from the airport proper), other than Enterprise, which seems to frown on one-way rentals around here. We found a rental car for $75 for a 24 hour one-way rental with unlimited mileage, and a drop off at the IAD rental facility. Then we'd just take the rental shuttles to the airport.

Just something else to throw into the mix.