I know of someone that paid 32.5k for their ring in the last 30 days.
I also know of another person who paid 30k for their ring in the last 30 days.
Price is pretty much what people are willing to pay. You might expect to pay a similar price as those two did, or possibly less, guess it all depends on what rings continue to come out. I've heard a lot of people saying that the Christmas 2017 ring is the #1 event ring. As long as it's a top ring, you'll probably have people asking for top price.
It wouldn't be fair to make these comments without pointing out that I own a XMas 17 ring, so of course I'm somewhat bias. Nevertheless, it's a fantastic ring, and if it's true that someone got one for 23k off the black-market recently -- props to them, I would say they got a great deal on it at that price.
Hope this helps.