For 800 Wii Points, players will get a 30 day subscription. 1,500 Wii Points provides access to Network Mode for 60 days, and a 90 day subscription costs 2,000 Wii Points. Each game comes with a 14-day free trial.
Why are the fees for a Japanese game that isn't being localized significant to us? Because this is most likely a preview of the pricing scheme for online play in Monster Hunter 3, which is being released worldwide.
Update: commenters are pointing out that Monster Hunter games have always been fee-based in Japan, but not the US. That puts the situation regarding Monster Hunter 3 right back up in the air. It doesn't change anything for G, of course, which is not leaving Japan.