I was looking at a company called SensorPush. They are a little pricy but most of the hardware and software is made in the US and it seems very flexible on multiple configurations (I think it’s intended for industrial applications)
HT.w Wireless Digital Thermometer runs about $70/ea and requires a base station. It doesn’t have a local alarm or external screen though which I don’t like as it therefore seems to require the phone to be useful. I’d run it on a separate WiFi network to be safe