I've been toying around with nebula, self host your lighthouse on a cheap VPS (which even if it gets hacked, the most it can do is lie about traffic, not lie about node certs). Basically you're just paying for the punchthrough (you may even be able to do some duckdns shenanigans?) The main issue is that updating nodes is a pain in the butt, which is the main advantage of tailscale IMO - centralized control plane. Keeps it simple.

I was trying to do some kind of insane workflow where you as the operator have a privileged hardware yubikey that admins the nodes when you plug it in, and the point is the nodes would self-propogate the changes outwards. I immidiately ran into classic issues with distributed security in distributed systems (even with only one central operator trying to admin everything). Tailscale is also a bit more secure in its oauth layer - with this architecture, you need to set proper time limits for expiring so one node compromise doesn't get access to the whole fleet. Couldn't really come up with better ideas than forcing the operator to reuse some kind of hardware key (the idea trying to be avoiding maintaining a cloud control plane as much as possible)

Fun foray but creating such a system requires a lot of expertise that I unfortunately lack