Tube Amp Pricing

I’ve been curious about the costs of tube gear. As far as my layman eyes can see, the components in tube amps look similar. And yet, the pricing is all over the place - $30,000 to $1,000. Is it the amount of engineering that explains the wide differences in cost, the components, or a combination of the two? Just curious

Engineering, components, and place of manufacture will all factor into the cost.

Obviously, it cost much less to engineer and manufacture in China than in the USA.
The schematic design of an amp drastically changes the sound. I prefer the sound of single ended amps, although have also enjoyed triode & pentode designs. Also, even though (in some cases) the basic components appear to be the same, there are different levels of quality with them. For instance capacitors vary greatly in cost depending on brand, as do transformers, resistors, tubes, & wire. All of these can change the sound of the amp. 
R&D, low unit volume to amortize the fixed costs, and piffle (aka, audiophile tax)

audiophile gear is subject to some concept in economics called reverse xxx - as the price goes up, sales go up

the classic example is BMW cars in the 1980s where sales were fueled by yuppie desires for showing off a luxury product (in the early to mid-1970s, my 2002 was relatively unknown and priced about the same as Olds)

somewhere I saw a video of Audio Research amp construction - maybe a factory tour - it shows how they are built (laboriously), the careful selection of wire & components, and the testing of each unit

Harman Intl. has an extensive laboratory used for audio testing (but are a very large conglomerate these days so it is affordable)

those 2 examples show good reasons why some things cost a lot
There's many way over priced tube amps, just as there's many over priced speakers, cables, dacs, name it. 
Like much of high-end audio, the price doesn't always reflect the quality and performance. Much of this industry is built around the sucker, and as they say, there's one born every minute.
There is probably an asymptotic relationship between price and performance. Some circuits are simple (ie., SET) and use the fewest components; others are much more complex. Individual components then become a factor - silver wound transformers, for example. Then there is the economy of scale.
Wow thats a tough one its the quality of the parts and construction of the unit also were it is made that helps determine the price.
While there are plenty of tube amps that one could call over priced the reality is it's hard to make a truly good tube amp cheaply. Parts cost can be quite high transformers in particular can be quite costly and are critical to an amps overall quality. Other parts such as capacitors and wiring can also be rather pricey. Basically  in an amp with fewer parts the quality of those parts is even more important. Also the relatively beskope nature of these amps makes them that much more expensive, parts are bought in small quantities and cost more. Sometimes even vintage or very specialized parts are used. Factor in build time labor and a solid markup and you start from a fairly expensive "floor" cost. It's when you start seeing glitz and glam on amps and marketing hype and technobabble that prices start to skyrocket.
This question comes up periodically.  The answer in good part lies in the aesthetics.  The faceplate is often the most expensive element.  Then the rest such as the capacitors as mentioned, some use large banks of them, then volume ladders and other resistors, wire transformers  and so on depending on the design.
Thanks for the responses guys. It has been enlightening. Competition being what it is, I kind of figured pricing was where it should be.
I doubt it is where it should be(!)

Benchmark is an xlnt amp for $3k - I'd like to see the reliable listening tests of amps that can 'beat' it.

At some level one might select resistors carefully (maybe after caps, active devices, transformers, circuit design, etc.), so see this:

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I would imagine the quality of the tubes could also be a factor.  A Chinese 12au7 costing $10 vs. a NOS Mullard for $300.
I’m no model “Mr. Green” when it comes to conservation, but I’m astute enough to see when excess goes so far beyond the bounds of tolerable waste that it deserves dishonorable mention. Truly, some vacuum tube power amplifiers merit that distinction. Other forms of “conspicuous consumption” pale when compared to the staggering inefficiency that you enable when using a stereo power amplifier that features eight (or more) hi-power vacuum tubes in its output stages.

Listed below are basic performance specifications for three closely comparable stereo power amps. One is solid state, the other two are premium vacuum tube power amps. Take a look; compare the data. Also, be assured that what’s shown is entirely representative of equivalent product offered by other makers. The specs are as extracted from the relevant source's website.

(1) Parasound model Halo A23 (solid-state) stereo power amplifier: Continuous full power output = 125 Watts (x2) into 8Ω, 200 Watts (x2) into 4Ω, 20 Hz - 20 kHz, both channels driven.
Total harmonic distortion: < 0.06% at full power output.
Power required: 25 Watts in standby idle, 700 Watts at full power output into 4Ω loads.
Mains fuse (USA): 6.3 Amperes.
Street price: $995. ea. (Audio Advisor, on-line site).

(2) VTL Amplifiers Inc. model ST-150 (tubes) stereo power amplifier: Continuous full power output of 150 Watts/channel is loosely claimed, but conditions of measurement are not specified.
Specified power output = 120 Watts into 5Ω (driving both channels assumed, but not specified).
No power output ratings were provided for 8Ω loads and 4Ω loads.
Total harmonic distortion: < 3.0% at 120 Watts into 5Ω load, 20 Hz - 20 kHz.
Power required: 240 Watts* in standby idle, 800 Watts at “full power” (no conditions given).
Mains fuse (USA): 15 Amperes.
Listed price: $12,295. ea. in Canadian dollars (Melbourne Hi Fi, Victoria, Canada, on-line site).

(3) VAC (Valve Amplification Co.) model Phi 300.1a (tubes) stereo power amplifier: Full power output of 150 Watts claimed, but no conditions specified, so refer distortion measurement (next).
Total harmonic distortion: < 3.0% with 135 Watts/channel continuous avg. power at 1 kHz into         a 4Ω load when connected to the 8Ω output tap (stereo mode).
Power required: No power consumption stated. It’s likely slightly > than for VTL ST-150*.
Mains fuse (USA): No info provided.
Listed price: MSRP $22,000. ea. (Scott Walker Audio, on-line site).

*Both tube amps draw more power when in standby mode than a 55 inch Sony LED/LCD TV set does when in use. Note that 240 Watts standby is equivalent to continuously burning four 60 Watt incandescent light bulbs without shedding any usable illumination—just generating lots of heat.