Why not? Musk specifically stated during the revelation of the Superchargers that it would be possible to travel from LA to NY in a Tesla car for free in 2 years.

I'd bet a super small subset of their customers will ever take a 4 day drive. They will fly, it would be cheaper.

Cheaper? Not sure about that. I've done a couple 3000+ mile drives and the price was pretty comparable to a flight (in terms of fuel). If you have more than one person in the car, it's cheaper than flying.

And these are electric cars we are talking about. I would imagine they would beat the cost of flying every time.

but you must not forget, time is money.

Of course. And don't forget you need a place to stay and food to eat on the way as well. I was just referring to the cost of transportation.

How would it be cheaper if the refueling stations are free?

Hotels, food, etc. If the goal is the destination rather than the journey, I imagine airlines will be the most efficient form of long distance travel for the forseeable future.

How much will flying cost in the future?

It's not appropriate for people who want to do cross-country trips, just like a pickup truck isn't appropriate for a single college student with nothing to haul.

Oddly enough, I fit that mold pretty well.

But I have a Nissan Hardbody, which is a small engine truck. Good gas mileage, reliable as hell.

I like it.