go to config and open item search for saphire amulet
when you find it it should look something like this
item = 1687 Sapphire_amulet It's_a_Sapphire_amulet 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0
change where it says 1 to your price so it should look like this
item = 1687 Sapphire_amulet It's_a_Sapphire_amulet 10000 10000 10000 0 0 0 0 0 0 0 0 0 0 0 0
save compile and you are done