The French post website is: http://www.laposte.fr
You may wish to set up a redirection service. Complete a leaflet obtained from the Post Office. It’s free and the post will give you 10 free national postcards to notify your friends of your move.
The price of stamp (in 2005 - for a standard letter of 20g maximum) was 0.53 € in France (red colour) and 0.55€ (blue colour) for Europe (that you use for any European country).