If you’re okay with just text communications, the meshtastic project is also an option. Because it uses LoRa for communications, nodes can be further apart. As

If you’re okay with just text communications, the meshtastic project is also an option. Because it uses LoRa for communications, nodes can be further apart. As a bonus, it allows for encrypted [1] communications as it doesn’t use licensed spectrum. But, LoRa is a low bandwidth technology (or at least meshstatic is), so text is about all you’d get. But it works with pretty cheap components. [1] I’m not sure if the algorithm has been vetted or not.