I don't know if it's been mentioned about costs, but I contacted a private mint, and they said for a custom silver coin, the minimum order amount is 500, and custom die making costs anywhere from $300-1200...
So to sell a custom silver coin, we would need at least 500 pre-orders, at the current spot price alone is almost $20,000... So that might be why he hasn't released anything in silver yet.

Yes, you've hit some of the issues. However, I think I have a way to do silver. They would probably be half ounce coins. And I don't think I'd have to resort to pre-orders.