Regarding silver weapons, it may be mainline GURPS Dungeon Fantasy rather than Dungeon Fantasy Roleplaying Game, but
GURPS Fantasy Tech 2- Weapons of Fantasy has official rules for precious metal weapons. They boil down to "when a 'silver' weapon is worth less than its weight in silver, assume the +19 cost factor buys enough silver on the business-end of the weapon to deal with vulnerable monsters; if you
insist on a 100% silver club (or sling bullet) add the price of the weapon's weight in silver to the base price of the weapon, treating this increase as a cost factor so it isn't further multiplied by other weapon modifiers".