Sure, there's a huge variety among private trackers. Googling "buy private tracker invite" shows 10s of different sellers. some tracker invites can be $150 because they're gigantic communities full of content and don't send out invites often. Some of them are cheap enough to throw in as freebies when you buy something else.

What's really nice about buying an invite is splurging the extra $10 and getting a built in 500-800GB of quota with it (really you're buying the account itself). Then you don't have to "work your way" up as long as you keep seeding whatever is popular.