I've been at this for over 21 years.....here's my thoughts.....
There have been several attempts over the decades to standardize the costs on vintage computer equipment. When I was 14-15ish (1997) I went to visit my sister in Idaho, went to a computer museum in the region, and bought a book of blue-book values for vintage computers, most of the stuff we cover here was still over $100-500 in value (XTs, ATs, 386s, some early 486 machines). At that point, I Was not yet a vintage computer guy, I was a guitar guy by and by large only.
2001 happens, I start accumulating 486s like there's no tomorrow because everyone is jumping on the XP bandwagon - mostly for free. People were GIVING Them to me because they did not want their old DOS machine anymore, they wanted a Pentium 4 with Windows XP on it. Anything Pentium 90 or higher was going for over $100 still. SVGA CRTs still asked for a good $40+ at Goodwill, bug VGA or EGA or CGA was just a few bucks.
2005 rolls around, prices on IBM PC, XT, and AT class sysems start going up. Up till that point, a 286 was a "free" item because nobody knew what to do with it. In that time frame, I bought a barebones Deskpro 286 for $24 that looked like hell and had been sitting in a guy's garage for several years. My Deskpro 386 was over $50 and sold for $75 on E-bay when I sold it. I bought my GEM 286 around that time for $34.00.
2010 is when I got out of things for a little bit. LGR was still a small fry, 8-bit guy was still the macbook guy, at that point, I was the only person I was aware of on YouTube doing any amounts of DOS computer stuff, and by that point I'd kinda' left that because my guitar stuff was way more popular, and I was tired of most people chastising me for having a pile of old PCs and that I should "junk em' and get a AMD Athlon/Core 2 Duo with Windows 7".
Then during my absense, LGR caught on - and I was stil lhankering to at least have one old 486 box around to mess with. What has happened to vintage PCs in the last decade is what I predicted during the 2000's would happen and almost gave up on that belief. I mean, in 2010, only a handful of us were messing with old stuff like this, and it was not YouTube driven, we were the outliers of the internet....but buy 2015, the pool had grown, you had LGR Oddware/Thrifts/Things, Macbook Guy was now the 8-bit guy, Adrian's Digital Basement started to crop up not long after, Phil's Computer Lab shows up, NostalgiaNerd, and of course me (Creepingnet), VWWestlife, and a few other older YouTubers were still around doing things, at least in my case, periodically. That's when I really started to see prices shoot up.
At this point, I don't even hunt for old hardware anymore. One thing in this hobby that easily turns into a "trap" of sorts is when this stuff was plentiful we got tons and tons and tons of it for next to nothing. When I lived with mom, I had 32 x86 IBM Compatibles at one point in various stages of (dis)repair ranging from fully working and kicking butt to barely a barebones box with a working motherboard. When I started my channel, I had an entire floor of my closet taken up with old 8088-Pentium laptops and desktops. Today, I still kinda have that but the mix keeps getting weirder these days.
I still sell on E-bay and try to keep things reasonable so that parts of my collection get out there and still get a good home from time to time. I have seen a few machines I've sold in the 2000s and 2010s pop up on there again every so often. A DEC 486/33 I repainted in 2003 (bad yellowing, pre-retrobrite) popped up in the last year, it's crazy, I sold it for around $15.00 in 2005, but it was going for $100x that almost - for example.
That said, I still come across a good bargain once in awhile. When I moved where I am now, I was GIVEN a NEC Ready 9522 tower, but I hardly use it. I've had co-workers give me a lot of 2000's era stuff, and I still, in our town full of thrifts, find the occasional 486/pentium system in some dank, dark corner of a thrift shop somewhere that most people would be too scared to walk in to because it's in a roughter part of town. Sometimes I just bump into things visiting little mom and pop computer shops, or doing things like I kinda did with New2U computers which was talked to the manager and got an opportunity to check out some stuff that went through. BUt being as I'm almost 40, have a career, and a wife, I don't really have as much time as I used to to be messing with jumpers on cards....these days I prefer to enjoy what I've got, not chase after more hardware I have to tweak and tune and fix.
I think these open-source projects are the future for retro-hardware. As the pool of old stuff dries up due to overpricing, hardware failure, recyclers, and whatnot, to keep these old boxes going were going to need to look to the future to keep things sustainable. Some of it is an opportunity to enable us to have more room options in the future that are not just merely emulating on some Raspberry Pi in a custom enclosure.