Each capacitor is hand built and sold in very small quantities.
I have been very lucky and have been privy to capacitor comparisons done at a speaker maker I know. He has 4 levels in his speakers - Erse - Erse bypassed with Duelund VSF Copper - VSF Copper and Cast. You can easily hear the difference with each level - its an increase in speed, clarity and naturalness.
I heard comparisons of two speakers both exactly the same except one used Mundorf SIO and the other Duelund VSF Copper. I listened to Patti Smith - Gloria with the Mundorf's - her voice was low, arresting and guttural - you go wow - but it did not sound like a normal female voice. Then the Duelund - it was not as arresting or as guttural, it sounded more recessed, you think its not as good as the Mundorf - but you notice its more natural and faster - things sound more life like. You go back to the Mundorf and you realize its false.
Forget the Silver - its a personal preference thing - some love Silver others like me don't like it - unless you really love what Silver does save your money and get copper. The speaker maker I know has checked it all out and doesn't even offer silver as an option - if you asked him he would build you one as a special order but at a much greater cost and you may not even like it - many, possibly even most, don't.
Regarding cost the Cast version of the speaker the manufacturer I know costs $13.5k. Expensive - yes - but there are many many much more expensive speakers out there. Personally I have not heard a speaker even close to that speaker regardless of cost.
Thanks
Bill