Have you consulted
Aéroport Marignane : Liste des aéroports de France, parking aéroport de Marseille Provence ?
An aeroclub ACMP is mentioned there and elsewhere, they seem to have had a website at one time.
But have you also checked the landing tax as mentioned at
Nav 3000 - euroVFR : tools for pilots, 3500 airfields. ? Though I'd like to see that confirmed.