[kefka]

And I have gotten my base IoT node down to about 2.50$. How?

Arduino Nano ($1.80) nRF24L01+ (0.63$)

Both from Aliexpress. Combine it with MySensors library and off you go.

For secure connections, use the USB-serial gateway, change the default channel, turn on encryption as well as signing support.

I use Node-red to get the data and do stuff with it.