Because of my inability to access information from my heat pump, I designed and built a Low Cost Energy Monitor
A lot of caveats! Particularly when it comes to safety. Mine’s been working for a couple of years with no problems. 2 years ago, when I built it, it cost under USD$20.
Works with MySensors Potentially it could run as a gateway to avoid the nRF24 radios. But then it would have to be plugged directly into your HA host or use a wireless serial cable.