To add to the bit about searching for parts, that's one of the things that pushed me to start really researching what I'm buying before I buy. It's made twice as hard because I can remember all sorts of previous trends in vintage PC pricing back when people had forgotten about these machines or made fun of them. Only certain makes/models have parts available, and have those parts available in quantities that don't mean they would only make sense ordering if I was setting up some kind of shop.
Like back when I first started diving into laptops in 2003, I could buy generic/off-brand 486s and 386s all day long for the price of a song on e-bay, but good god, if you ever wanted a memory upgrade, or a power supply, or batteries, I had to dig and dig and dig and dig. And if it still had parts availible, people were probably still using the device on the daily. I remember mid 2006 when I bought my first IBM ThinkPad (755CD) and remember being totally elated to find out that I could get updated Lithium Ion batteries for it (instead of NiMH). That's party of why I picked the machines I pick these days when I have a choice, because I can still get parts for an NEC Versa.....but a Compaq Portable 486c is like finding a needle in a haystack for ANYTHING regarding that machine. That's why I sold the latter off to another collector who had parts. Yet thanks to Asian distributors and the fact that NEC sold that screen to other companies to use on their machines long after 1994, I can find plenty of screens for those, plus other parts (motherboards, power boards, batteries, power supplies, keyboards......).
I probably spend 3 1/2 years chasing a 128902-001 640x480 Sharp TFT LCD for that blasted thing, only to give up and be willing to pay up to $100 for one from one of those sites you find surfing the web looking up part #'s. THREE places said they had it "in stock" - two e-mailed back stating they don't, and one did not even get back to me. When I did find a place in China with one, they started spamming my e-mail box with plastic molding machine parts - none of which were the parts to my portable......and yet other places said they would ship for $189.95 or whatever, and it would be for 10 of them - I don't need TEN laptop screens, and I don't need to take that kind of gamble on a then 25 year old computer that I only need ONE of that part for.
Another frustrating thing is chasing drivers! Like recently was trying to find drivers for my 40EC and my M75 before it arrived - It took 2 weeks of surfing and LOTS of digging for the ftp.necam.com on archive.org after finding out their FTP died sometime late last year. Sheesh. Sometimes if it's really rare - like the MediaVision ProGraphics 1280 card I had years ago, I had to dig and dig for 2-3 years before I found the drivers, and the only way I found them was I found the one of four or five people on any forum who knew that card and had the drivers....only to find out the card was fried. That's why I'm now storing these things all over now so people can still get them when I'm done with them. However for web sharing, the cloud has made it a total nightmare. Then sometimes drivers have an OEM specific extractor (looking at you NEC) so you have to HAVE a product of theirs to extract for another product they make.
Recycling networks are owned by resellers who pull everything of value. Retro computing is a huge business. Asian countries always sit on huge stockpiles of new old stock and they can flood the market with obsolete parts when it suits their needs
Not only that but a lot of PC parts, especially screens on laptops and even some planar assemblies from the 1980's-1990's were used in industrial equipment, SBCs, and Embedded applications, so you also have these scores of chinese clone part makers and recyclers that o nly sell in bulk for large prices because they are designed to cater to the Industrial market. Those frustrate me when looking for parts because I don't need 20 NL6448AC30 640x480 TFT LCD screens at $1,996 a crate, or $80 cases of light pens based off another 1980's PC design. Also, some of those places falsely advertise they have the parts availible online, but never pull the listing for the sold-out inventory and then tell you they don't have it in stock. Also, I don't like that they often use a picture of another part to represent the one they are selling and it makes it difficult to tell if it's the right part or not - and at some of the prices they are charging, it's almost a gamble to be sure you are ordering the correct part.