I own 2 groups one with 2715 members and another with 1657 members I can put url of your website and one line text for $15 per month in the footer of both the groups (Maximum 5 links will be sold) you can also buy footer link for group2 for $7 per month and group1 for $10 per month So everytime a message is posted in the group, it goes to most of 4272 members via email, so if 30 posts are made in a month, your url is advertised to so many members 30 times. Also it will remain visible for a long time in the groups.