I am almost sure that somewhere out there exists/existed golden coned speakers with diamond baskets. However, just because they exist I don't think such items would reflect the cost of a top end audio system because same or better sounding items are available for more reasonable prices.
In terms of head units, the most expensive is the $1000 Pioneer PRS head unit... you can look it up, and my understanding it's worth its features to a lot of people. Subs, probably Morel Ultimo, which costs $600-$800 a pop.
Speakers..?
With so many SQ competitions won with HAT gear, I won't consider anything more expensive than HAT Legatia speakers worth its price. If your 3-way front stage ends up costing more than $2000, that's certainly a rip off.