i actually dont know too much about this web can you tell why its so good that invitations are so expensive?
This is a private tracker, meaning the announce used for the torrents is inaccessible for the non-members.
The private trackers have a benefit of being faster than the public trackers i.e. kickass, etc. since everyone there uses Seedboxes (especially the uploaders) and the downloaders have to abide by certain rules to stay a member, which forces them to seed back or else they are banned.
Hence an ecosystem is well maintained.