It's just too expensive where I am to buy NOS any more. As I build my own amps I like to use JJs and tune the amp to the tube. It's fun and affordable (except the bit where I can't afford to buy amp parts from the US any more and even tubes are becoming crazy expensive). The bits which are affordable are the bits where I swap the odd cap and resistor to change how the amp responds.
Even JJ tubes have skyrocketed in price in the past few years. I generally buy my tubes from the US but that's becoming scary $$. A basic JJ 12ax7 used to be US$8.95 not that long ago. Now they start at $16.79 at Antique. I guess one good thing I have discovered recently is that I like the sound of my fixed bias amps at 60% plate dissipation. It sounds good and my tubes last a lot longer.
If you use a Matchless or Bad Cat you might want to check how hot your tubes are biased. A friend of mine has a Matchless Lightning which goes through power tubes at an alarming rate. From the factory Matchless seem to bias their cathode biased amps at 110-120%. 100% seems to be the sweet spot for cathode bias and to me it not only sounds better but helps your tubes last longer and your amp to run cooler. I don't know why they bias so hot. It really doesn't sound that good to me. It sounds too glassy and bright, and cooling the bias helps the amps sound warmer and improves breakup in my opinion. Once you get below 90% the sound of the break up starts to sound worse again.
A lot of tweed Deluxes are biased too hot too. It's because the cathode resistor value is based on '50s wall voltages. When you get a 5E3 biased properly the difference is astounding. No more compressed mush past 9.00 on the volume!