Ask HN: What's with the DIY state of the art long-range Wi-Fi?
Reach out to various existing infrastructure projects that build and maintain large community-owned P2P WiFi deployments, the two largest ones are Freifunk and Guifi. They would surely be able to and wanting to help you, if you reach out to them. Try https://freifunk.net/en/contact/ and https://matrix.guifi.net/Most of them are using commodity hardware from Mikrotik, Teltonika and Ubiquiti. Basic setup for a personal node is just an antenna + router. Then they usually have the concept of "supernodes" who are responsible for hooking up multiple personal nodes, and have uni-directional antennas + multiple ones + bigger routers to facilitate the routing.I'm not sure you'll be able to put together a supernode with decent range for under $100 though, think the cost would be more than that, but I would be happy to be proven wrong.In terms of firmware, I've almost exclusively seen OpenWRT being used (and the rest running default Mikrotik/Ubiquiti firmware), with various self-made patches done to it before installing it on the hardware.