Ads on a huge FB group?

Suppose I had a group of 2,000,000 people on facebook. A GROUP. So I can't send out messages, but I can post links on the main page and tons of people will see it daily. How much do you think I could get/where should I advertise my group to?

Thanks

well since its a social network site promote a dating site.

and place the link there.

yeh i do this but you dont get much clicks to be honest. unless its niche related to your group. also make yourself a fan page for that group. this way you can message all members. unlike the group