Problem of tracking Daily Energy Cost because price is not static

Hello

I have a contract with tibber so my price per kWh is changing by the hour. I want to Display how much Energy cost i have per Day. On my Dashboard for example. So with a Static price i would just calc used kWh x price per kWh but since the price is changing i dont now how to track the individual price per kwh. I have a entitiy for the Price which is updated by hour and i have entities to monitor kWh usage. Also im using NodeRed.
Can any body help me?