How expensive are best NOS tubes ? And how difficult to find ?

the expense is mainly in picking thru 1,000 tubes to match 10 very closely

there is a video on how Audio Research turns a cheap tube into a spendy hand-picked tub - same for caps, etc.

I have a very simple solution: I buy ARC tubes for my ARC gear (!)

I let their engineers do the jobs they were assigned to do.

Then I pay them.

That’s exactly right, randy. Finding the cream of the crop will cost the consumer.
I have a very revealing single-gain stage preamp and needed to return some microphonic 6SN7 tubes to Vintage Tube Services. Andy replaced them and told me that he needed to test 60 tubes to find a pair that he considered high quality, (and they fetched a premium price).

I find the price well worth it for my current CD Player and previous preamps, as the tubes can last a long time, not so sure about some high power tube amps...as for the engineers picking tubes, while I trust them, they are limited to tubes available in very large quantities, not NOS tubes...

I've had very good luck with new production Chinese tubes.  The Shuguang and Psvane tubes are excellent.

you can find good tubes when buying used or from stock that is inconsistent.

for example, the EI or yugo 12ax7 tubes. Used to be $3 each. You could buy 20, and maybe 5 or 6 were ’perfect’ and a VERY good 12ax7. Keep the rest as useful scrap.

Trying to ace one single used tube batch buy, is a waste of time. Average it out over lots of buys. You’ll be strongly in the positive that way.

the second thing, is you needed a tube tester and the ability to hear the tube.

Specialization, or skill increase in these areas is not that difficult to come by.

You can sub in thought and effort --for money..., if you put in the effort and time. Caution: learning curves apply. There's a whole world of tube lore....

New tubes are finally coming on line and working out fairly well. They are starting to get pretty good.

But some classics are pretty well the best, like NOS Telefunken diamond bottom. When you hear them, you know it. Those are in the "f-me!" category (when you hear it).

We used to be able to pull them out of old dynaco PAS preamps, like welcome candy on a good day.