It's not really hype. A single transformer alone can cost > $50 and you might have two per channel...and that's just the tip of the iceberg. Tube designs are more complex to manufacture and can require more QC. Really though they're not necessarily much more expensive than comparable solid state preamps...in fact tube preamps are not the norm, and it's not a tube that makes a preamp expensive. You can find very used neve and ati solid state preamp modules UNRACKED (e.g. no power supply, no nothing, just a circuit board) for $200-500 or more.
For a long time I thought just like you...that it was all name brand hype. But then I started looking at some schematics and pricing out components. I found that in order to build what would probably turn out to be a decent preamp would cost quite a bit of money...more money than a "decent" preamp could be bought for brand new (manufacturers get their parts in massive quantities, remember).
Yeah you might be able to make a copy of some $2000 preamp for half price, but you probably won't have built as good a preamp! Any audio circuit is more than just a collection of compatible components. If it were that simple, I would buy up as much behringer stock as I could!
It's more than math. Guys like rupert neve have designed preamps based on years and years of study....trial and error...listening and listening and listening. Your basic amplifier circuit can be found in any beginners electronics book....but if you think that's all that's to an expensive preamp, you're wrong!
And IMO there really is no "vintage" craze. It's simply a return to *quality* sound. 30-40 years ago if you went out to buy a guitar amp, chances are you would be looking at a decent piece of gear, regardless of your price range. Then along came some great leaps and bounds in electronic & manufacturing technology, and along with em came all these companies cashing in on it....your crates and your peaveys and the like.....with some bizzare consequences too. Prices of quality gear seemed to go up, perhaps to distinguish it from the cheap stuff, while prices on cheap crap continued to drop. Perhaps it was also to distinguish a "better" manufacturer's good gear from the cheap crap they too put out to compete with the peaveys and the crates. You see this phenomenon all over the place. Then the digital age came along and things got even more out of control.
What none of these new guitar players realized, myself included, is that while they could plop down $150 and bring home an actual working guitar amp - it sounded like shit!!! Did we know it sounded like shit? Nah, we're still trying to play "ode to joy". Then we get to a point where we realize, "hey, I don't sound as good as I think I'm playing"...but do we dump the cheap amp and buy something that we think sounds good? Nah, you start tossing all sorts of garbage boss effects in front of it because they're cheap. Why pay $800 for a new amp when I can get a "distorto screamer 8000" all-in-one digital programmable effects box for another $150?
Then one day you wake up and smell the coffee...and you're stuck with all this cheap garbage. When I say "you" in this case I really mean "me." Thus when I shop anymore I am indeed often looking for "vintage" gear deals, but simply because a "good" guitar sound really hasn't changed all that much, and I've got a better chance of finding a good deal on something that's 30 years old than something brand new.
In the meantime, here I am with my POD and my peavey amp and my garbage effects and my cheap mic preamps and my cheap microphones. Maybe next time I'll get it right
Anyways, it's really the cheap gear "craze" that has caused the complete misconception that ALL gear is cheap to make. It was and is the continuous onslaught of nearly-false advertising and bogus claims. How many times have you heard a salesman say that some cheap piece of gear sounds almost as good as some expensive piece of gear? Oh man. How many magazine ads have you seen to that effect? How many times have you heard people complaining about the "vintage" craze? How many of them were either broke and frustrated or salesmen?
This isn't all to say that there isn't a lot of overhyped gear out there. I'm just saying that if you bargain hunt and look for manufacturers who put out quality gear at reasonable prices, you probably won't be able to DIY for much cheaper. Only go the DIY route if you're really super interested in learning about the ins & outs of audio electronics.
Slackmaster 2000
