I think your find what we pay over spot is pretty darn cheap just compare to say copper bullion ...just going off the NZ mint site I see the NZD spot Silver price is $24.57oz NZD with a selling price of $28.26oz now that gives them a $3.69 gross profit per oz they must take out process costs , freight of the metal, GST , etc
Idea of process -https://www.youtube.com/watch?v=t0_egjO1EEY