I guess the US Government / Air-force, and other launch customers paid for the launch since they have active Falcon Heavy contracts with SpaceX. This test was part of the certification process.

I'm pretty sure that Tesla didn't pay anything for the advertising. It was Elon's own Roadster. If you look closely, the Tesla logo wasn't included in the Falcon Heavy launch promotional video: https://www.youtube.com/watch?v=Tk338VXcb24