Check out the new IKEA Matter over Thread stuff. They have two smart plugs (an indoor single plug and an outdoor double plug). You can flash one of the esp-idf example images to an ESP32-C6 and plug it into your HA server to turn it into a Thread Border Router for under $10. Everything on Thread uses a fully local encrypted mesh network that by default has no Internet access (leave NAT64 turned off in the HA border router add-on).

P.S.: Make sure to update the firmware on the devices (which HA can do), as several don't act as routing end devices until after the first upgrade.