"In der Anzeige stand, der Kurs koste nur 90 Euro" - Is the omitted "es" supposed to be the Subjekt, and its verb is "stand"?

Hallo zusammen!

Yeah my question is basically in the title. Omitted "es" in German always drive me crazy.

"In der Anzeige stand es, der Kurs koste nur 90 Euro"

Thank you!