Technology Required for Licencing

Wow, those are tight specs for the cost points. To get electrical components like strain guages (pressure transducers) to operate at those tight specs over normal variations in temperature, you will need significant ($$) signal conditioning and compensation. The process for producing the transducers to operate within the tolerance band will be challenging as well unless you are willing invest in labor intensive factory calibration. Ultrasonic sensors are challenging as well due to the propogation velocity changes of sound in air based on barometric pressure, humidity, and temperature.

Seems strange to need a level sensor to accurately measure water height to within a millimeter. Did you mean for it to be 0.01% precision or absolute accuracy?

Dear Brave Sir Robin

Actual requirement is 0.1% for temperature variation from 0C to 70C operating temperature. Level sensors often provide an average value due to layer fluctuations and temperature compensation. Pressure sensor is dipped in water or fluid can easily compensate for temperature variations within 0.1C to 0.5C. Yes, ultrasonic sensors find it difficult as they are away from fluid.

Sensor may cost $10 and electronics, another $10 and perhaps packaging and cable etc another $30. I think it is possible to build such sensor effectively for under $100 for volume production. This is not only realistic but factual for most of the manufacturers. If you buy such sensor in the market then it may cost $400. Manufacturing to point of sale has many overheads that push the price.