FWIW the food industry might provide an option for you. Digital thermometers are typically either thermistor or thermocouple and remote probes allow reading outside the environment being checked. Just walk up to the tank and press a button for an instant reading or, leave it on, and it can sound an alarm if a temperature is exceeded. A good one is less than $50 and accuracy is really quite good.
Find me one for under $50.00 that would stand up. I know a huge blueberry farm and processing center that would love cheap stuff.
Any communication protocol to get back to a master?
Usually ain't cheap to rig something like this up.
