You need to throw out your fossil-economy preconceptions. Efficiency is irrelevant when you're running off direct solar energy. Sure, you could drop the price of a complete unit if it can run on a smaller panel, but the significant variable is not energy efficiency, its resilience to intermittent insolation.
It takes up space in the boat, it requires labor to extract the ice. If you're buying 10 times the boat and 10 times the labor the price is going to have to support it.
This is why Tudor ended up in debtors prison before he got the business model right.
At southern or tropical latitudes often 90% of the product would melt before it made it to market. Insulation was primitive (saw dust).