Paul:

Tubes are actually as cheap or cheaper than they were in the 1950s, adjusted for inflation. Most are either made in former eastern bloc countries or in China. The quality of the Russian tubes is excellent, as they used tubes in their military equipment until recently, maybe even still do. One potential problem is that there are fewer tube types being manufactured now. It has settled down to the most common power and preamp ones being in abundant supply, and inexpensive. If you buy a used or 'vintage' tubed product, it is good to first look at what kinds of tubes are installed, and see if they are still being made. Stupidly, there are a couple of current amplifier manufacturers that buy up a good stock of obsolete tubes and design their new amps around them. Then you have to purchase any replacement tubes from them at whatever price they ask. Not a good way to treat customers.