For small range (few km) you can just utilise LoraWAN for free communication.
This is a technology that is very interesting to me, but I have not gotten my hands on it yet. I know there were some Italians who had gotten some 100s of km using LoRa (I think it was testing for the Guifi network)
> could be accessed in the area
If you didn't want remote access you would not have to pay rx/tx costs.