It would have to be a huge cost savings ($250 or more) for me to even consider getting in a car and driving to the airport. I am a $15 cab ride to DCA, but a $65 cab ride to IAD. I will only use IAD for nonstop international flights. Any other airports within 100 miles of DC (RIC and CHO) generally involve either a connection back through DC or a connection through a hub where I would connect from DCA, anyhow. I guess there's BWI, but it's a massive hassle to get to and a terrible airport.

When I lived in central VT, I was 75 miles from BTV, 100 miles from MHT, and 150 miles from BOS and BDL. I did very occasionally fly out of BOS for transcons, but that was about it.

The savings generally don't make up for the extra time and inconvenience.