Cost, Insurance and Freight - the value Ghana Customs charges duty on.
It is the price of the goods, plus what it cost to ship them, plus the insurance. People budget on the invoice and are surprised at the port, because freight on a single container can add more than the duty rate does.
Worse, the invoice is not the last word. Customs values goods against its own database, and where a declared value looks low for the item, the higher figure wins. This is routine for vehicles and for anything commonly under-declared.