I have received recently a few emails from you asking me some advice about public transport in Paris.
If you plan to stay in Paris for a week, there is a pass that costs around 20 euro (for zone 1-2) and that gives you unlimited access to metro, bus and RER within the chosen zones. It’s a real value for money, if you think to travel a lot around Paris. To compare, one way ticket costs 1.7 euro. Please note, that you also have to buy a plastic card (5 euro) at the ticket office before charging the pass.
If you stay in Paris for a month or longer, I can advise you to buy a monthly pass that is about 70 euro (depending on zones). The the same process as for the weekly pass: you should buy a plastic card at the ticket office and after that charge the pass.
For students under 26, there is an imagine R pass (from 27 euro per month) which is valid for a study year. To obtain the pass you should fill in the form (ask the agent in the ticket office of metro), send it and wait for 3 weeks until you receive your pass. Please note that the demand should be made before December.
Unfortunately I learnt about the existance of Imagine R 3 months after my arrival in Paris, so don’t waste your time, and once you start your studies, apply to your Imagine R. More info on www.imagine-r.com