The aviation world has similar stuff. In the US, the experimental homebuilt scene is great. Lots of us (myself included) buy a kit and build and customize from there. My build is a kit from Vans Aircraft (likely the biggest of such manufacturers), but other companies sell kits and even just plans to build to your heart’s content. As the builder of record, you’re free to build and customize things like engines and avionics without being a certified mechanic.
Not popular enough that I've heard of them by name, but I also don't tend to dabble with rotors. I prefer my engine up front, and my wings to remain stationary to my person. Also, if you think fixed wing is expensive, wait until you see how much rotorcraft go for...
