Well, we know that the invites were "on sale" for those prices, but do we know if there were actual buyers?
Anybody can put a price on an item in the online market. And yes, it only takes one newbie to pay too much, or to pay for something that could possibly be obtained through barter, or free via a generous act. So, perhaps those high prices are just that -- prices.
Really? I didn't realize that. I registered for one of those invite sites once. But it was such a big deal just to get one invite, I left. Everything is a racket. No one should be any invite! This is one of the reason DMCA goes after these trackers. Clearly their making money asking for "donations."