Good cable design has many different elements as mentioned. Just talking about silver vs copper is part of this picture. I’ve recently been using both Zenwave all silver ICs (latest version of the D4) and power cables. These cables use OCC silver which was designed to minimize grain structure in the cable. In speaking with Dave at Zenwave, he has experimented with many different aspects of the cables to get where they are right now.
He does make OCC silver speaker cables and yes, they are expensive. There are definitely price differences in different levels of “pure” silver or copper.