Sorry to resurrect a months-old post. I missed it first time around, as I've only recently joined the wonderful Audiokarma community. And I'll offer another view, that no one has mentioned here.
I recently signed up because I bought my first-ever classic receiver: I picked up a Pioneer SX-750 on eBay. Paid about $460 for it including the fairly expensive shipping. And while some of you may consider me stunningly foolish for doing that, it was worth every freaking penny! It looks great and sounds fantastic--and I can improve both, even though they're already quite good, by putting some new veneer on it (the old vinyl is still in very good condition) and at least recapping it and giving it a clean, although right now it doesn't seem to need much of either. I'm 60, but I hang out with considerably younger folks (I teach a bit, and do a lot of photography, particularly music and sports), so I know a bit about what they're thinking and doing.
I bought my Pioneer not out of just nostalgia--I never had a system like this before, couldn't afford it, so I've generally always listened to music on cheap crap, so I'm not reliving an experience I had in my youth. I just have always admired the look and sound of the old Pioneers (and some other systems) of friends who could afford good audio gear. But even though my new (to me) receiver is over 40 years old, it's still a very useful part of the 21st Century, as I'll get to shortly.
As I mentioned, I'm a photographer. I do obviously shoot most things, particularly if it pays, or moves, or has to be shot in tough light, digitally. And that's great. But I started off in the days of film photography. And I still love to shoot film. When I started, I used a Minolta, and a battered old Nikon F4 (great camera, but it was pretty worn when I got it). Eventually, I became able to afford "better" cameras, like a Leica (I have two), a Rolleiflex, a Hasselblad (got three of those!), a Mamiya RZ67, and some large format stuff.
I was lucky I bought all that before the prices on *those* things started skyrocketing. I could easily sell most of my camera gear now for two and approaching three times what I paid for it. If I hang on to it longer, it'll go up even more--I don't see the prices on that stuff coming down any time soon. And I don't see the prices on a lot of classic receivers dropping soon, either, although I think you'll still often be able to find bargains on that, by diligent searching, than you will on old camera gear.
Why are prices surging, and going to *remain* high on classic cameras and receivers? Well, several factors, and these apply to both camera and audio gear:
1. There is a constantly diminishing supply. Nobody is making these anymore, and losses from lack of new parts, house fires & accidents, stuff getting tossed out when people die cos their relatives have no idea what it's worth and not wanting to be bothered, etc., mean they are slowly becoming rarer and rarer.
2. The remaining ones, in many cases, can be repaired, and remain in use--and many people, like me, kind of like the idea that some of our devices have histories different from ours. Someone owned them before us and enjoyed them, we will get great use out of them, and if we care for them properly, they will carry on being useful and bringing joy after we are dead. Most camera techs who service film cameras are getting all the work they can take on (and making very good livings), and I'm seeing more and more young people wanting to learn how to work on cameras--something similar is going on, from what I can see here, with old receivers. The idea we might buy a camera/receiver and it be ours *for life*, and be passed on to someone else later if we look after it responsibly, carries value.
3. Many older devices like these are "better" than some modern gear simply because what they put out gives you a look/sound/feel that cannot be emulated completely by "modern" devices, and which people find appealing in its own right. I don't personally know many audio geeks (no offense intended; I'm definitely a camera geek) because of the circle of people I move in. But I know *loads* of young photographers who've found they really like the aesthetic, the process, and the output from film photography, and so now *they* are buying up old cameras, which drives up prices. And these aren't just "hipsters." My most recent studio was in West Orlando, which is kind of the "hood," and I encountered many young black photographers, most from less privileged backgrounds, who are committed to shooting film despite the extra expense. And I spent 11 years before that shooting in London--I knew loads of young non-hipster photographers there, too, who shot mostly or exclusively film whenever they could, many of them whose work was getting published; it gave them *artistically* the look they were after. The "warm" and "musical" sounds of many vintage receivers are quite desirable, and not just for nostalgic reasons. And, given the next point, lots of people (including many younger people) are learning about and then competing for these items, driving up prices.
4. The internet. Camera prices are significantly driven by YouTubers and other "influencers" (aaargh, I hate that word) with huge followings who extoll the virtues of certain cameras, making them very desirable and pushing up prices. I don't think quite the same thing is happening with audio gear, *but* you *can* find out anything practically you want to know just by sitting at a keyboard. I made the decision which receiver I wanted not by stumbling across it at Goodwill or a flea market/garage sale (who has time to do all that nowadays??), but by researching it. I settled on the SX-750 because I learned it had the combination of sound, looks, features, power, dependability, repairability and affordability that I wanted. I found all that out courtesy of the lovely folks at Audiokarma and elsewhere. Then, once I made my decision, I could have waited around forever to actually find a good one in my area, which would have been cheaper certainly. But hell, I'm getting old! And eBay is right there.
So instead of going on dozens of fruitless quests and checking out units of dubious condition, functionality, and provenance, I could look for one from a knowledgeable seller, in the condition I wanted and at a price I was *willing* to pay. And my purchase would be covered by PayPal's buyer protections, something not available on a flea market find. (The thing about buying on eBay that makes it even more expensive is the shipping charges and taxes; the actual bid price on my receiver was only about $350, which I considered quite reasonable given current prices and the quality of what I got; shipping on this heavy beast--the seller went out of his way to pack it securely--and taxes added on almost another $100 to the total, so I can't really be mad at the seller for those--he only pocketed a bit over $300 after eBay fees.)
5. The ability to use these great old devices with modern tech. I develop and scan my own film (including color, when I've got my JOBO unit out of storage), but most photographers I know--particularly the younger ones--just send their film out for developing and scanning. And when they get it back a week later, they can push it out there by posting it on Instagram, e-mailing it to art directors/editors, or whatever. If you've got a big IG following, waaaaay more people will see your work nowadays than back in the olden times where you had to produce prints, and then somehow get them in front of your audience. My old Hasselblad film gear can be used with a digital back--and in fact, that's how I did most of my studio work. I could shoot something with the amazing old Zeiss lenses for that camera, and then deliver it to my customers or post it online almost instantly. So I got the enjoyment of using a fantastically good old camera, with its brilliant, huge viewfinder and more precise focusing, but I could output it in a 21st-Century way. And because the sensor on the ancient (2004 vintage) digital back I was using was sooo much larger physically than modern DSLRs/mirrorless cameras, I could routinely kill the quality of most images produced by the latest Canon/Sony/Nikon stuff--the images have a very filmic feel to them, which is different from what you get with the latest technological wonders.
In the same way, you can use classic receivers *with* modern ways of listening to music. For example, I use a Mac Mini as a video and music server. I've got the sound output of the Mac connected to one of the tape inputs on my SX-750 (I use my TV as the monitor). So I can play my entire MP3 music library through it, I can stream anything I want through it (right now, I'm listening to BBC 6 Music online), and I can use it as my sound source when streaming movies, too. I just got back from a visit to a friend in Atlanta; he's got an old blue-faced Marantz, and he has plugged into it a Bluetooth device that allows him to stream anything he wants from his phone or laptop directly to it. So we're using modern electronics, but the music sounds *so* much louder and *better* played through a vintage receiver and proper speakers than it ever could the ways we'd normally listen to it with those devices.
6. Receivers are good entry points. Yes, as many people on this thread alone have mentioned, you can actually get *better* sound from separates, and more cheaply in many cases. But that's a step beyond what most people are ready to take when they first get into the field. A receiver combines everything you need in a form that's simple enough to understand and get to using quickly. It's kind of the same thing in photography--you'll get better quality, by far, from large format gear. But that hasn't shot up in price in the same way that lots of 35mm and medium format gear has, simply because it's *too* complex and intimidating (even though the cameras themselves are quite simple) for most people to deal with. While loading a roll of film into a 35mm/MF camera is easy, and many of those cameras take care, in a rudimentary way at least, of some of the thinking process with built-in meters, aperture priority, autofocus, etc.
TL: DR - Good vintage receivers, just like classic cameras, are rapidly increasing in price for reasons beyond simple seller's greed, and they probably will continue to do so rather than dropping any time soon.