To move something in the air inherently uses more energy than any sort of ground transport. To make the aircraft more efficient, you have cut weight, which means more exotic (i.e. expensive) materials. The powerplant has to have a higher power:weight ratio (again more expensive). It's more dangerous to be flying, so you need additional safety equipment that ground vehicles don't need. Etc, etc.
And if any aviation technologies manages to gain price/performance better than the stuff used for ground transport... it will be adopted by ground transport. Which still leaves air transport more expensive for the reasons listed above and many others. Hell, in WW2, they stuck an aircraft engine into the most common US tank (sherman). Interestingly, sherman tank crews didn't have to worry about falling out of the sky and dying if their engine failed (though they had lots of other worries, of course).
Long story short: there is nothing magical about electric motors turning propellers. And battery energy density is utterly horrible vs gasoline/kerosene. Air transport will ALWAYS be more expensive than ground transport. Perhaps someday it will be cheap enough to be common. But personally, I doubt that such a day is anytime soon.
Last aside... You can buy a small used two or four seater plane NOW for < $100k. Get a pilots license and you can fly around to your heart's content. General passenger aviation today is not reserved for the ultra rich.