What does 90% of the Absolute Best Sound Cost?

In the end, it depends on how much obsessiveness and pathological compulsion dedication and commitment one is willing to bring to the table.

As @onhwy61 rightly pointed out, a purpose-built listening room becomes a necessity if one is to even hear the difference better gear makes. Yes that room can cost $250K+, though it doesn't have to.

I don't have a dedicated listening room and I don't want one. I sometimes listen to music 12 hours a day so I need to do something else at the same time, namely, in my case, work. That supposes, by definition, a very imperfect room, which in turn limits how much better gear I can get while still reasonably hoping to hear significant improvement. But I wouldn't last an hour a day in a dedicated listening room before I got cabin fever, so I'm more than willing to live with what I have as it lets me listen to music for another 11 hours, and at the end of the day listening to music is what I'm here for. 

@mattsca

After a certain point more money gets you bigger and louder scale appropriate for larger rooms. Larger rooms need much bigger speakers and amplifiers and even multiple amplifiers.

In smaller rooms with nearfield systems you can get super high quality audiophile sound for a much more reasonable price.

What size room are you talking about? 

90% costs about $100k new, not including room tuning and best record pressings.

The best sound costs about 200k, I say that because that is probably an average of what professional playback equipment costs (only digital). The room is extra. 

Agree with Avanti1960

i have a <$4k near field second system that is 90% of my more than 10x $  main system in their respective environments. 

but I could not replace my second system in its larger environment and be anywhere in the ballpark.