I'm fairly price sensitive when on personal travel, but being Downtown and choosing between IAD or DCA seems like an easy call for DCA. Washington Flyer cab or a roving RedTop cab will cost you close to $70.00 each way.

That negates the value of your voucher.

You could take the 5A, but that takes a fair amount of time and luggage space is very limited.

Not to mention security lines, traffic, congestion, etc.