Orly Paris Airport To Boulogne Billancourt Via Rer And Metro?

Hi. I am looking for the mose economical way of getting from Orly to Boulogne Billancourt (Port de St Cloud) via RER and Metro. Is it RER B from Antony to Danfert-Rochereau, then Metro 6 to Trocadero then Metro 9 to Porte St Cloud? Is there a faster way?