I'm having trouble envisioning exactly what you're asking for / thinking about trying to do.

So split it up:
Looking for the lowest cost.
Looking to use CNC for some reason.
Looking to generate low build time.
Looking to have builders work together to build multiple copies, with some benefit of that to be defined.
Create a new design that meets ? objectives...

My impression is that "open source" for a whole NEW aircraft design is impossible. Nobody's going to agree what the objectives are, and unless there's an arbitration board (or Office of the Chief Engineer) or the like, it will just diverge in a bunch of different directions.

Besides, if creating a new design isn't really the main objective of your inquiry, why not support one of the plans vendors out there? They worked many, many hours, built test parts, flew stuff that didn't work so well and worked it out - all to give you the rights to copy their success for just a couple hundred $. I'm sure they'd be thrilled to find out you have gathered together 10-20 like-minded individuals willing to stand on their shoulders to get into the sky.