The best, longest lasting, most repeatable, and still quite cheap method is to use a pressure sensor in the top of an inverted cup. Make sure the bottom of the cup is below your lowest liquid level and make sure that the cup itself is filled with air and does not leak. In this setup, the air pressure in the cup is dependent on level of the surrounding liquid. There are some issues to be addressed with corrosion due to high humidity in the cup, but these are not too difficult.

Arduino is a widely popular microcontroller platform that can be easily integrated with various types of water level sensors for monitoring liquid levels. The choice of water level sensor depends on the specific requirements of the application, including the type of liquid, the range of level transmitter manufacturer, and the accuracy required. Ultrasonic level sensors, pressure sensors, and capacitive level sensors are commonly used with Arduino due to their ease of use and availability of libraries. It is essential to select a compatible water level sensor that can provide reliable and accurate measurements to ensure the optimal performance of the system.