Can anyone help me to get from Airport Paris-Orly to Porte Clichy with the cheapest way possible?Metro?RER?

So i will be arrived from Hannover at the Airport Paris-Orly at 20:45 at night. And I have booked a hotel room in Ibis Paris Porte Clichy Centre. Can anyone help me how to get there in cheapest way as i must save as much as i can (i'm a student)? My friend told me to get RER and then Metro. Until when is this... show more So i will be arrived from Hannover at the Airport Paris-Orly at 20:45 at night. And I have booked a hotel room in Ibis Paris Porte Clichy Centre. Can anyone help me how to get there in cheapest way as i must save as much as i can (i'm a student)? My friend told me to get RER and then Metro. Until when is this RER still running? Im afraid when the filght get delayed or must wait very long for the baggages then there will be no more RER. Or maybe better with bus? And is it very hard to find the RER/bus/Metro station in Orly Airport?
Thank you very much in advance.
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