Expensive Tube Amplifiers

I think the OP is a little misleading.  Yes, you can buy a vintage tube amp on eBay and restore it, IF you have the experience and knowledge to do so (plus a few hundred, maybe more, in spare cash lying around.)  You also have to know what you're buying, what kind of condition it might possibly be in, and the complexity of what the restoration might involve.  When the ad says, "It works!" that can indicate a wide range of condition issues.  Over on another forum, every week you see a thread that usually starts something like, "I bought this Fisher XXX on eBay but it hums and the output tubes are turning bright red.  How do I fix it?"  Those with experience do their best to walk the new owner through a diagnosis and possible fix, but it gets a little scary when the new owner says, "Which are the can caps?"

Another thing to consider is that the vast majority of classic vintage tube amps are limited to 35 watts per channel or less.  If you need power, you're much better off buying a Black Ice, Rogue or Prima Luna.

From my perspective, having run tubes since 1973, the biggest cost is the glass. I had a pair of Quad IIs restored--units from 1959 and 1961 and found a matched quad of GEC KT 66 NIB/NOS. Impossible to find these days. My Lamm ML2s were pricey new, I paid less than full freight back in the aughts, tube cost is a grand, add another grand for NIB/NOS Tele 12 ax7s. 

I like tubes. I still have my ARC Dual 75a which I bought new. It is not in service, but I’m sitting on a full complement of tubes I bought back in the day from ARC along with various parts-- like barrier strip terminals. I’ll restore it when I need to, last time it was gone over, fresh caps, etc. was circa 2003. 

These units can last a lifetime. Of course, you have to use them in the right application. These various tube amps are not suited for all applications. The Lamms drive Avantgarde Duos, an extremely efficient speaker. At 18 watts each, they are not an "all purpose" amp. But overpriced now? I have no idea, since I’m not shopping for new gear. That, in some ways is the point---you can enjoy these things with proper maintenance forever. The best glass is harder and harder to find, though. 

As always, Roger Modjeski’s mighty fine Music Reference amplifiers are completely ignored. Not by the likes of John DeVore, who has an RM-10 in his system. The RM-200 was Michael Fremers' "moderately-priced" tube amp for over a decade.

A couple more makers of (relatively) moderately-priced yet (very) high-performance tube amps are Mike Sanders of Quicksilver Audio and Tim deParavicini of EAR-Yoshino. Roger and Tim have unfortunately passed on, but their amps occasionally show up on the used market.

Regarding Quicksilver, guilty as charged.  Excellent amps at reasonable prices.  As for "vintage" amps, I assumed the OP meant amps from the 1950's-60's.  I would argue that buying a "classic" amp made in the 80's or 90's could be just a problematic as a Marantz or Fisher.  You can run into obsolete components or scarcity of proper schematics.

Larry, I consider Mundorf and Hovland caps to be birds of a feather, in the sense they’re both modern high quality film caps. I certainly don’t think all modern caps sound the same, and it doesn’t surprise me that either one is preferred over the other by a specific listener.