Each metal unit scales up by a factor of 100.
1 silver = 100 nars
1 gold = 100 silver = 10,000 nars
Also, 1 platinum (aka "white gold") is 100 gold = 1,000,000 nars.
The bulk cost of the mirrors was 350 silver = 3.5 gold (35,000 nars), but Sherry haggled it down to 3.0 gold (30,000 nars)...