Washington Dulles International Airport is not currently accepting reservations on AirportParkingReservation
$10.00 doesn't seem too bad for a big airport like Dulles. I agree the shuttles can be erratic, but overall, a good parking situation.
Plenty of shuttles but they stop frequently for no reason. Then they wait for 5min. Not a problem unless your spouse likes to be late then go crazy because something "took too long". The price is very high but it's more reliable. If you are capable of budgeting your time there are other, much cheaper, places close by.
Very difficult to find parking and the shuttle does not come by often.