Dalibor makes a good looking large nixie for less £££/$$$ New New Stock, Tested with 10 years warranty - and I suspect that we shall see more new manufacturers of tubes coming to the market (like the ZIN-18's from Millclock) as interest in Nixies grows. When I joined the FB group Nixie Clocks Fan page - there were about 700 members, now there are 2000+ members.
We have all watched the price of NOS tubes rise steadily as interest has grown. Look at IN-18's and Z566M's for example - I have seen their price rise by around 20% over the last few years. As for B-7971's - I came to that party particularly late but their prices seem to be rocketing even more recently. I have been fortunate to be able to purchase what I need at a price that was ultimately acceptable though to wholly tolerable!
I guess its like most things, a lot of us will may wish that we had got involved earlier on when prices were a lot smaller etc.
Some say that these things go in cycles - I'm not sure how long it will be before we once again see B-7971's for under £10 a pair but I suspect I'll not be in the market for them then :-(