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

Inna
Andy really is a cool dude and can tell stories about sourcing good stock - that itself is like a global
episode of American Pickers

it does or at least has helped me to build a relationship with a trusted source - Andy for me and start to lay wines into the cellar for drinking later to follow thru on my prior analogy - I have 4 Tube components so I have a few and importantly a path to move along...

Glen, this is certainly a good point, I am not sure how to figure it out when it comes to power amps. I would not be concerned much about phono stage and line preamps. Of course, another obvious point is how many tubes you need for a power amp. Tubes in preamp lasting for a decade if you are lucky ? That's great. In any case, I will most likely start with phono preamp, it makes sense to me.
Tom, I heard there is a Navy ship junkyard in Russian Arctic. How do tubes react to cold, by the way ? Maybe Andy knows, about the junkyard I mean, and the cold. I bet he's got an interesting line of work.

I just want to add a vote for NOS or lightly used tubes, but I can see that the benefits might not be worth the trouble and expense for many people. 

Well, real audiophiles are not many people, they go the extra mile.
But money is tight these days, anything audio I buy - I have to cut the expenses somewhere else. Still, $300 bottle of French wine once a year is something that I can do.

One of the reasons why you will find a wide variety of opinions on vintage tubes comes from the fact that most tubes sold as NOS are really just old tubes where the amount of prior use is unknown and wildly variable.  Even when someone has "tested" the tube, that does not say very much as most tube testers can do little more than tell you if a tube is near dead or not (something like the modern Amplitrex tester which tests at full power gives a better picture).

Speaking very generally, many varieties of vintage tubes tend to have a longer life than modern tubes.  Given the high cost of many of the more desirable vintage tubes, the decision on whether to go that route comes down to how much one likes the particular sound of a tube, how much one can budget on replacing tube, how averse to "gambling" on disappointing one is and how hard is your equipment on the tube.  On the last point, some gear run tubes conservatively and certain tubes will last seemingly forever when not driven hard.  With that kind of gear, it makes more sense to splurge on the good stuff.  I have an amp that runs four 348s and four 349s, both of which I can find substitute tube types that cost a tiny fraction of the price of these tubes, but, I don't use the cheaper alternatives because the amp has been running for years with the same tubes (which were probably old when I got the amp).