It is a MMO so you have to pay monthly fee. The price per month is afaik like the other MMOs too, like about 13Euro or Dollar.
If you pre-order, you should get the game a bit earlier, if you want to play it (i think) 3 days earlier then the release, you have to pay for it. Was about 5 Eur/$ for 10 days, and you can play 3 days before the big start. But you have to activate the full game after this 10 days, then the 30 days coming from the game will start, and after this you have to pay per month.
Just read a bit on the official site or boards