Since I have pretty much arrived at my personal end game solution I have not set out to find an end game speaker and I haven't really considered price as I listen to all manner of speakers, but I think the $15K for a pair seems about right. After this you pay a lot for very incremental improvements.
Agreed again, and luckily for some hitting live music level peaks is either not desired or not possible due to their living situation so they do not need to wrestle with that. I am not a head banger, but I do occasionally "air it out" and having a system with virtually unlimited output capabilities is desirable for me and was a goal in my quest. This eliminates ALL small speakers regardless of cost.
This is also exactly where I'm at now, after a long-ish journey via several well-known (but not always good-sounding) speaker brands.
There's a cost for large speakers that are engineered to have flattish on-axis and smooth off-axis response and that don't get shouty when driven hard. That cost seems to be about $15K (GBP12K over this side of the pond).
Also, I do think that digital room EQ has made the task of finding the right speakers a bit simpler. We now know which speaker behaviours we can equalize and which we can't, and this makes the list of criteria for speaker choice a bit shorter.