I looked into this, and it seems to me that the pricing is going to end up being about the same as WoW, just with time limits that are not very constrictive.
1-month card: 19,800 won (approximately 13.7 USD*), 300 hours for 30 days
3-month card: 47,520 won (approximately 32.9 USD), 900 hours for 90 days
3-hour card: 3000 won, (approximately 2 USD)
30-hour card: 12,000 won ((approximately 8.3 USD)
Basically about $14 for 300 hours in 1 month. That's 10 hours a day, every day. I doubt I would ever go over that.