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

It has been a very long time since I've even looked at the price of the tubes I run.  They have been running for a long time without going bad.  I run six Western Electric 348's, four Western Electric 349's, two Western Electric 310a's and two Westerh Electric 310b's in my amp and linestage.  My headphone amp runs four Telefunken EL34's.  My phono stage runs two tubes that I can't recall the number, two Telefunken ECC803S tubes, and two 300b (Gold Lion) tubes as rectifiers.  I don't know the numbers for the linestage and power amp rectifiers.  The 348 and 349 tubes are very hard to find, and pretty much all that are available are used tubes that "test strong."  Prices vary quite wildly with tubes from reliable sources selling for as much as $2,000 each.  The 310 tube has also become somewhat expensive to ($400 and on up for Western Electric versions).  The ECC803S has become ridiculously pricey; I saw a seller of supposedly NIB tubes asking for $3,000 a pair.  While I have not ever had to replace any of these tubes, the year that I do have to buy new tubes will bounce the average quite a ways up.

I have yet to throw away a tube. I have purchased a few and it's been a few years since my last purchase. So averaged <$100/year. Tube gear includes a headphone amp, phono stage, preamp, maybe 10 tubes total. 

I heard that some Western Electric and Telefunken tubes run forever. $3000 a pair might sound ridiculous but you buy them once, if that’s the tube that you really want.

In most years no expenditures (needed or not) for tubes. I test all tubes periodically. I had some VR105’s go and some 6AX4’s go this year and they are inexpensive, even with marching. One Linlai 300B drifted way out ouf spec and I replaced the quad of the Linlai 300B‘s with a quad of Takatsuki 300B’s. That cost 3k and quite possibly the best tube roll ever experienced. Good from the get go and stunning after some hours used. A glowing report. 
 

This year $3200 spent. Last purchase was a spare quad of KT170’s three years ago

I bought a new matched pair (consecutive serial numbers) of McIntosh MC275 Gordon Gow Commemorative edition amps, the first re-release, in 1993. I used them configured as mono blocks to drive my Martin Logan Quests. Though the amps came with Richardson KT88’s made in LaFox, Illinois and Chinese 12AX7’s and 12AZ7’s, after about a month I replaced the Mac-branded tubes with Sovtek 6550’s and NOS Mullard 12AX7’s and Westinghouse 12AZ7’s. When I finally, and regrettably, sold the amps in 2012 because of a move to smaller digs, the set of tubes I installed still tested as new, with both amps still outputting 90WPC in stereo exceeding McIntosh’s specifications.  These amps were used daily, not just for music, but for TV, too.  So no tube replacement whatsoever in 19 years. Good thing I set aside the original Mac tubes.  I nearly doubled my money when I finally sold the amps.