Just how much do you spend on tubes per year on average ?

My Cayin CS-845A uses 3 different pairs of tubes, 845, 300B, 6SN7. I use it as my amp. It plays 3 hrs/day. I change the tubes out every 3 years (3000 hrs). Last set of tubes 2025 were Psvane Summit series, about $2000. My preamp LTA Microzotl level 2 has 2 pairs of tubes, 6SN7, 12AT7. It is easy on tubes. So ... a long winded answer is $660/yr. That's using Psvane's best tubes.

Perhaps $300 for 2 years. Tubes last a long time!

I had a tube go south on my power amp the day after my earlier response.  The replacement price was $100, but I ordered a full replacement set for one of my two amps (about $ 700) and figured while I was doing that I might as well get the 18 tubes for my preamp, another $700.  Keep in mind that these are only spares and the existing tubes have been in use for over 10 years.  In other words, I wouldn’t let the replacement cost keep the OP from purchasing tube equipment.  

(OK I'll speak up because I do spend quite a lot on tubes) IMO My dollar amounts goes in bursts due to whether I get tube rolling fever. Plus, I'm an old SS guy who wants my tube kit quiet. Add to this, of course, I only buy NOS and seek out the off the main stream antique gems. Then there's the fascinating changes inspired by various combinations of pre amp tubes and power tubes. Some just sound much better in my system. Each has it own personality. At this time however, I think I've run the same combination longer now than all previous time periods. Maybe there were a couple years where $500 was normal per year. (Hey, I was learning what worked best) Plus its fun to be able to transform the complexion of the sound profile. Power quads can be pricey but they also last well. Unfortunately the old Chinese (1960's) sound best yet have about a two year life span at the pace I run them. At that point usually one will act up which gets the boot and I save good ones and buy a new quad. Dave Thompson of Raven Audio curates a great selection of gems for his "Raven Heads". If one has a Raven tube amp he provides the quality stash. Several other good tube sellers besides. Fun hobby