What is the cheapest way to get into air? (no jokes please)

Ditto. Powered paraglider. No need for a hill or a thermal. It packs up
better than any other aircraft. Initial investment is fairly low, and
so are training and maint. costs. And its an expanding sector of the
aviation market. Its kinda like the dark side of "the force" for me,
since I'm already committed to HG's and my pioneer-era machines. But it
definately meets the set of requirements you posted.

You might also be interested in taking a look at:
www.ushga.org

Harry