I have thought of the fact that a monk's body could be enchanted like a weapon. Here is a quote from the PF book. In conflict with this is the Amulet of mighty fists. I know one would have to take stacking into effect. yet a monk could cheaply enchant their body instead of paying huge amounts to buy an amulet
"A monk's unarmed strike is treated as both a manufactured weapon and a natural weapon for the purpose of spells and effects that enhance or improve either manufactured weapons or natural weapons."
"amulet of mighty fist grants an enhancement bonus of +1 to +5 on attack and damage rolls with unarmed attacks and natural weapons.
Alternatively, this amulet can grant melee weapon special abilities, so long as they can be applied to unarmed attacks. See Table: Melee Weapon Special Abilities for a list of abilities. Special abilities count as additional bonuses for determining the market value of the item, but do not modify attack or damage bonuses. An amulet of mighty fists cannot have a modified bonus (enhancement bonus plus special ability bonus equivalents) higher than +5. An amulet of mighty fists does not need to have a +1 enhancement bonus to grant a melee weapon special ability."