Calculate cost for the pool heater

I have a binary sensor showing when the pool heater is starting/stopping (binary_sensor.bwa_link_hot_tub_heating) and I also have a sensor.electricity_price_xx (Tibber).

I know the heater can consume 3kW when running. I’d like to create a graph of the cost per day/month how much the heating costed me. I totally understand that it might not always be 3kW consumed, but at least it will get me the idea of the cost. When running its running for 30-35 minutes more or less so that also needs to be in the calculations. So, with these sensors, how do I do?