A lot of things are cheaper when you have the RSA, but granted, it’s mostly leisure and optional things (museums, cinema, holidays at ucpa.com, etc). (ucpa.com is an excellent sports camp address for 18-40, by the way).
Not only optional thing. Metro/bus/tramway are nearly free for them. They also have reduced rate for utilities.
Granted it is not easy to live with 500€ a month, but you can get by.