• As a few people have pointed out, people often buy sunglasses for fashion and social signaling rather than on price. Wearing Tom Ford glasses means you're getting very good quality glasses, but mostly you are paying to wear Tom Ford glasses, in the same way that a Rolls Royce and a mid level BMW are functionally very similar, even though there is a 5x difference in price (if not a higher change). You're paying for the styling and the brand name.
• Where the money goes: for a lot of consumer brands, huge sums go into brand advertising. B2B companies spend this money on salespeople and tradeshows. I like to give the example of a Rolex. A new Rolex is worth $10-15k (if not more) because they spend tens of millions of dollars every year telling us all that that's why they're worth so much. Compare that to a lesser advertised brand - say Tag Heuer, and you'll see there's a pretty big difference in their pricing. Traditionally this money has gone into magazines / billboards / tv commercials / sports sponsorship - so this money is subsidizing middle class entertainment. On the B2B side, if you engage with a company like SAP, you'll get a professional sales team walking you through the buying process (they'll probably even spot you a few nice dinners along the way).
• "Rent seeking" is an interesting term, and while I agree with it in the context of sunglasses, it's a bit hard to nail down in a lot of the economy. Price is funny because lots of the things we produce now (particularly software, pharmaceuticals & entertainment) have revenue models that don't see much of an increase in marginal cost once you've covered the initial investment (10k people see your movie in cinemas vs 1m - provided you've got the infrastructure in place, it's not like the price of producing the movie goes up 100x).
• The culprits for the "middle class burden" is often pointed at healthcare and higher education for the simple reason that they have dramatically increased administrative costs which ultimately haven't added much (if any) value to the consumer (people argue my first point with regards to higher education - perhaps a Harvard education is worth $60k a year, although it's hard to see many other colleges worth that much for the brand alone).