The cheapest we could have flown is about $200 per person (2 people), not to mention taxi/uber costs.
So for one person, it might be a wash, but for 2+ people its very much cheaper to drive.
For example, I can fly round trip from Chicago, IL (ORD) to Miami, FL (MIA) for $325 per person (tax included, no checked luggage) taking about 7 hours each way (45 minutes to airport, arrive 2 hours early, 3:15 hour flight, 15 minutes to get situated, 45 minutes to destination). To drive that would take 21 hours and 1,400 miles each way which would cost about $300 in gas for my vehicle. This is really a best case scenario for flying being potentially as cheap as driving. If you want to fly to any smaller international or regional airport without frequent direct flights, the cost can easily be a couple hundred dollars more per person.
Mind you I'm from Europe, our gas prices are 4x as high and for trips to e.g. the UK or Scandinavia we have to cross a body of water. There's some toll roads too in e.g. France, and Germany wants to introduce those too.