I have 7 Mitsubishi heat pump head units being controlled using ESPHome running on D1 mini clones (ESP8266). The D1 mini clones are powered by and interface with the head units with Mitsubishi's CN105, which is just 5 volt UART.
The total cost was maybe $30 of parts on AliExpress.
I use 433Mhz Acurite temperature sensors with a software defined radio (rtl433) running on my Home Assistant box to have remote temperature sensing. The 433MHz sensors are cheap, have good range, and have excellent battery life.
Are you doing temperature control by yourself or are you feeding them to the Mitsubishi units as a remote temperature reference?
I know the Mitsubishi "wired controllers" (basically the official thermostats) can provide remote temp to the unit and the unit has DIP switches to select between thermostat-reported temp and internal return air sensor temp.
I'm not sure if CN105 has a way to provide this temp ref - if so, you could try it. Just make sure to set your wired controller (if any) as a "secondary" controller (otherwise it will also send its temp every second and overwrite the one you sent) and then set the proper DIP switch.
The total cost was maybe $30 of parts on AliExpress.
I use 433Mhz Acurite temperature sensors with a software defined radio (rtl433) running on my Home Assistant box to have remote temperature sensing. The 433MHz sensors are cheap, have good range, and have excellent battery life.