Is it possible to find a good DAC for under $50, 000?

Naaa. I got one for $49,000, and yep, crap. Shoulda popped for the extra grand.... 

It would need to have at least 10 cabinets per side.  Half dedicated to power reproduction,  then 2 128 CPU servers with 4 nVidia 5090s to use AI to re-imagine the music at a billion samples per second with 256 bit resolution. 

I mean seriously, if your DAC didn't cost half a million and raise electricity prices for the rest of the state do you even like music?

OP "...It’s about whether there is a point at which sensible effects cannot be discerned."

Good question. Not in my experience. I have heard well set up systems at price points out to the stratosphere... they are all very distinctive in terms of many variables. If assembled by competent audiophiles the sound directly correlates with the sound quality.

The trained ears / brain are capable of incredible differentiation of sound qualities. Audiophilia is about pursuing perfection. While the refinements may seem small, the overall impact is significant as music is nearly infinitely variable and complex (compare to a single tone).

I just upgraded to a Naim NP555 with its corresponding 555DR PS power supply. While it did not reach the dollar threshold of the unit in the video, it was a big acquisition for me. I could not be happier. My Cary DMS-600 was an excellent unit, but the Naim has shown me what I had been missing. The extended dynamics, detail, and soundstage are staggeringly good. I'm a hard core vinyl guy, but this is very nice.

Late to the party here. JMHO-A $50K DAC would most likely be surrounded with similar priced electronics, cables, speakers and a room with treatments. Therefor it is very likely that the sound quality would be more easily distinguished. So for that person it will be likely worth it to them.