What makes an expensive speaker expensive

Not really. The R&D, and design costs are fixed, but the number of units sold is not.  If you double the units sold, you cut your R&D investment per unit in half.  Now whether that investment actually produces "better" sounding equipment is another story altogether.

Bose used to have (may still) massive R&D spends, but they were laser focused on what consumers would pay the most for while spending the least.  It wasn't just about selling units, but about getting the ratio of price to cost as wide as possible. Not a bad strategy to make a company successful. The Bose Wave radio didn't just come out of a garage, it was tested and retested by consumer interest groups many many times.  Focal and other companies do the same, to various degrees. 

Lot's of ideas and in the end every company is very different.  Many companies are not that expensive to make, but they are large structures and priced accordingly.  Some give you a LOT of high quality components and hand made drivers with tons of R&D.  I know of two companies like this and both sound GREAT to me.  Every company has a different way to price.  The other thing I've mentioned earlier is that every company has a different points for the dealers.  I've heard numbers from 30% to over 50%.  That's HUGE.  When you hear of a dealer or manufacture selling for steep discounts, those are obviously the ones at or near 50% I would assume.  When you get a company where you can't get much if anything off, then they are probably much closer to the 30% profit margin to the dealer.  There is no right or wrong answer to this question, but it's a great thing to discuss and think about.

Having said that, I do think that really good speakers should and have the right to be quite expensive. But $100k ? Give me a break. You can buy a sure path to American citizenship for a little over $500k, and you won't lose anything in the end, it's investment. Now that's cheap. Going to be a million soon, as I heard.

Personally even if I had that kind of money, I'd never spend it.  The best speakers I've ever heard in a system are the Tidal (the big ones at well over 100k) and the Vandersteen 7 Mk 2's at 62k.  The only reason I can say the Vandy's to me are a great value is that they sound better (to me) than anything over their cost AND for only 15k more (or so) you can now get their dedicated high pass matching subs to make even bigger sound in your room if that's what you feel you need.  That's still only 77k total.  To me, that's paying off a huge chunk of my mortgage so that's never happening, lol.  For folks who can afford it, I'm very happy for them and don't blame them one bit for spending what they want.  They earned, or stole it so....;)

But...if you have a very big room and listen to orchestra and want great sound - cost of the speakers and amps will be much higher. Other than that, $100k for the entire system is more than enough, in my opinion. In used prices this would be, say, $55k. Still a lot of money but within the reach of many.