Silvers gone up. Golds gone up. Probably various fixed costs had to be further invested in the form of contracts with fabs or new fabs built. Etc. But really the Mac mini is more of a modern likeness to the G4 cube which retails now for a 800$ start, less than half the g4 cubes starting price.

Edit-they also went from being a company with around 8500 employees in 2000 to 137000 today. Surely every part of their organization chart has contributed toward pressures to otherwise push up their prices to maintain revenue.

Since Silver and Gold are priced in $USD their price is influenced by the actions of the US government. One of those driving forces is the current US monetary policies (i.e. an growing budget deficit).

Another factor is perceived risk. Since the markets are always worrying about the current US China trade talks, that uncertainty helps gold and silver as they are seen as safe havens.

Engineering costs, both in rate and quantity.