Amp design logic

Very good question!

The price of anything is always what someone is willing to pay for it. A $50K amp that has never been sold is not worth $50K, it is really quite simple.
OTOH some of the "best" parts prices (called components by manufacturers BTW) are higher than you might imagine . Look up Deuland capacitors for instance and think of multiples of that cost.
Labor/benefits costs also seems to matter greatly. I needn't tell you that some populus countries that are making most of the consumer electronics now, have very low costs. In fact all overhead costs energy, space etc. vary widely by place of manufacture.
Many things we covet are kept intentionally scarce and never marked down these have a quote a pride of ownership cost assiciated (Think Patek Phillipe, Cartier, ST DuPont) etc.) Certainly this phenomena is part of this hobby.
Don't forget patented proprietary circuit designs. A lot of manufacturers do not release diagrams (schematics) and code parts with their own numbers, making duplcation and reverse engineering very difficult.
Well that is a start but when you finish your perfectly built DIY $50K, for only ?$1K?? let us all know if it sounds as good as the original.
But in the end only the demand will ultimately decide the price.

You're right that the total components don't nearly add up to $50k. What you're basically paying for, apart from good design and execution, is for the most part the sheer mystique that such a product has - especially the mystique that becomes attached to it as soon as it's given a $50k price tag. You and I are clearly not the intended buyers for a product as this. We've spent at least some time getting to know audio gear to some degree in some technical way or another...that is, we've bothered to in effect actually glimpse the little man behind the curtain of this industry. And why did we go there in the first place? Because we understood that buying outright the kind and quality of gear that we knew would likely be necessary for us from the outset was going to be more expensive than we could afford...so instead of giving up on our dreams, we decided to figure out a way to do things as cheaply as possible ourselves and 'learn from the ground up' to enlighten ourselves as to what it would take to do more for less. We may have that kind of time, but there are others who are perhaps married to their careers or whatever who simply don't want to have to spend so much time, effort and energy just trying to figure out where to start. What they want is for someone that they feel has already taken the guesswork of it all out for them. These people may feel it a privilege of their level of income that they indeed don't have to bother with any of that. Their approach to audio