Expensive Tube Amplifiers

@devinplombier Oh, make no mistake, the Heathkit W2 was a notable amp.  Based on the Sarser-Sprinkle "Musician’s Amplifier’ which was the first American-style Williamson proposed in 1949, it featured a scaled-down version of the legendary Peerless S-265-Q output transformer.  Predictably, Heathkit took some shortcuts, but if you restore it to the original "Musician’s Amplifier" specs it’s a marvelous amp.  A midrange to die for and smooth high and low frequencies.  An effortless amp to listen to if you don’t mind the 20wpc limitations.  I've restored several pair of these.  In addition, I recently had the honor of building a replica of the original "Musician’s Amplifier" for the son of Melvin Sprinkle, using a Peerless S-265-Q I had in my stash.  He had never heard the amplifier.  It was quite an honor.

@dogearedaudio 

I've made a mental note of the Heathkit W-2, thanks for the tip. Meanwhile, these "Musician’s Amplifier" replicas are quite an interesting project.

PP vs SE many many Years passed I rejected SE Amp' and had PP Amp's commission built.

Today and only recently I have PP and SE side by side in the system and am struggling to reinstate the PP, as the SE is just so much wanted to be kept in use.

The OP refers to expensive Amp's in the Thread Title and then in the OP refers to $4K to $8K as a guidance on costs witnessed.

This is not expensive for Valve Amp's, when my PP Amp's were Commission Built the Output and Power Tranx's that were Bespoke Produced for the design and Hand Wound by a individual known for their skills, come with cost close to $8K during the 1990's. Large Hunks of Copper are not cheap, and Valve Amps thrive on such a partnership.

I have PP Valve Amp's owned and still able to be used, that fall into the price range referred to in the OP, and in comparison to the main PP Amp' they compare as being likeable but are discernible for their being very inferior for the End Sound capable of being produced. 

The loss of Prejudice towards SE has now got me revisiting SS Power Amp's, of which I have a design in my system at present and will be investigating another design shortly.

think the OP has forgotten inflation ran away for a few years. Everything went up. 

I own pushpull and SET amps and my current favorite is a very low powered 349 pushpull amp (around 5 wpc).  My SET is a parallel 2a3 amp. 

In the universe of amps I've heard, my favorite is a pair of custom-built OTL amps that, I believe put out only 20 wpc.  The owner said he "might" sell the pair if offered $250k.  My second favorite is a pushpull 252 amp that is also very low powered and would probably cost around $250k, but I don't know the current market rate (not much market activity for something like this).  In short, I don't think any particular topology is inherently superior and one can find many good examples of each type.