Thanks for your posts
I have decided to buy the Aegean pass, 6 flights CDG ATH, change until the last minute at the cost of 528€ + taxes.
It enables me to have a long week-end in Athens 25-29th May at a decent price : 243€ return.
It's a long week end for French people and prices were out of this world : 1067€ return in economy

All in all, for sure, it's a good deal ... and 2 more return flights within a year to enjoy more of Athens !