We know the Falcon 9's marginal cost for relaunch (with fairings reused is $15 million). Of this $10 million is for the second stage, $1 million is for booster refurbishment, the rest is for operations (including the landing barges) and fuel (which is $300,000 to $400,000 at the moment). These numbers are from Elon Musk's May 2020 Aviation Week podcast. I haven't yet found a good recent figure for the sticker price of relaunches though.

I did some analysis based on these numbers in this 8 minute video here: https://www.youtube.com/watch?v=36o4UrS9OS4