I have tube amps and have spent this year alone $1300 in tubes.Wow! Well, there are tubes and amps and there are tubes and amps. High power pentodes don't last very long. Triodes can last a long time but DHT triodes will degrade over time. But many power pentodes and tetrodes in well designed PP or SE amps just run and run and run. Tube amps can be very economical if you want them to be.
When I purchased a McIntosh MC225 a few years ago it still had the original power tubes from 1963 - and still does, despite playing several hours every day. I have purchased many vintage EL84 amps with original tubes from the late 50s and early 60s. Were these tubes better than modern? Maybe, but it's more about amp design.