Becoming an active member is completely free.
You automatically become an active member when you've made posts in at least 3 of the last 5 weeks. Activity includes uploading POI files and/or posting in the discussion forums.
The weekly posting periods run Monday through Sunday (Eastern timezone). Active member status is updated once each week (on Monday mornings).
If timing of your first post is lucky (Saturday or early Sunday), you can become an active user in just a little more than 2 weeks.