Whatever it takes to get a working prototype. There should be plenty left over from KK's high school experiments <smirk!><quoted text>
Plus citations from NALSA, a paper by an MIT aerodynamics professor, links to cites that go over the build in more detail than has ever been shown by any of the examples you list and none of them want your money. They have no means to take your money. I suppose you could hunt them down and give them some of your money, but they would not give you anything for it.
Eventually, I will probably build one myself, but my expectation is if it doesn't work in some way then "I didn't do it right" ... kinda like "praying".