I think sometime this year it is suppose to be released. According to Wiki they are still in Beta.

Quote Originally Posted by http://en.wikipedia.org/wiki/Ragnarok_Online_2:_The_Gate_of_the_World
Current Status of the Game

The first Closed Beta has officially ended (29/11/06 11PM GMT+9).

Details for when the second Closed Beta and the Open Beta is not yet known. However, an event involving participants who missed out on the first Closed Beta indicates that 2000 of these people will be invited to the second Closed Beta. Details of who is in the second Closed Beta will be released on January 8th 2007.
As for monthly costs, I have yet to see anything.