Most expensive

From what I've seen from my Chinese friend's magazines, they are probably custom made by someone we've never even heard of, only available in Hong Kong. Who knows - maybe some crazy expensive stuff in Dubai, too, but that's just a WAG on my part. Just imagine the wealthiest place on earth, that's where I'm guessing you'd have to go.
As far as comparing to other speakers, from what I expereinced at 2 CES/THE shows, there is little, if any, correlatiopn between price and performance. I went into room after room of good but not fabulous sound being played by equipment of all different price points. There were a few rooms that stood out, but they were't necessarily the most expensive rooms. Sometimes, I think you're just paying for the price.

I have seen speakers in ad's for up to $300,000 and I am sure thats not half of what some may cost but I would never want to see any of them as it would just make me mad. I dont and may never think that any speaker no matter how high the cost can be vastly better or even maybe equal to some for $50K and even hald of that, it just gets a bit silly after awhile.

The most expensive that I can think of are the Kharma Grand Enigma. I believe that there is only one pair, and they were installed in an underground room (large domed ceiling) somewhere in Europe. The price was quoted as 1 million dollars. I think you can google a picture.

No such thing - there is always a bigger fool - so today's most expensive speaker on earth will be surpassed.

FWIW - room acoustics quickly become the most limiting factor for sound quality. You can't put lipstick on a pig (the most expensive speaker on earth is never going to make a bad room sound wonderful)