Aero-engineers: why can't we make airfoil kits to make certain vehicles 'air worthy'? A 10k addon to your current sedan to make it short take off and landing sounds way more fun than anything else.

I understand that weight on ground for stability is completely different than air travel... but why not create a whole class of vehicles around this premise?

The only one I can remember is the SkyCar from Moller. He was a little ahead of the game with petrol based quad motors.