Oh, so much more lies at your fingertips. Extra damage is available, to be sure. But you could make the weapon highly durable instead, or load it up with a Magical Charge. Charges act as any one spell from the entirety of my magic system, but once you've spent it, it must be recharged by finding a mage of that caliber to cast it back into the weapon. With your money, you could only afford one charge from the cheapest source -- which would involve magic of the Earth, Wind, Motion, Parameter, Action, or Body variety. For the cost of 100 gp, plus the price of your hammer again, you could use the hammer to shift earthen materials, create a gust of wind or a deafening clap of sound, turn yourself super-speed, slow down the enemy's motion, alter how spacetime affects your hammer, or allow your weapon to grant you bodily mutations in some way.
Now if you wanted a Magically Damaging Weapon instead, see below:
If you made your weapon into a Crushing Magic Light Hammer, it will appear to burn or crackle with energy, especially when dealing damage. Every strike, the weapon will deal twice as much damage as normal.
If you made your weapon into a Magic Light Adze, it will appear to taper to an edge, which faces toward the enemy no matter how the weapon is held. When an effect would check whether the weapon's damage is blunt, the damage will count as slashing instead. You can also deny yourself training bonuses as use it like a handaxe instead.
If you made your weapon into an Impaling Magic Light Hammer, it will appear to resemble a morningstar when still, but seem to become bestial claws when swung. Instead of exchanging for slashing, it will exchange for piercing damage. You can deny yourself training bonuses to use it like a morningstar instead.
If you made your weapon into an Energy-Charged Magic Light Hammer, it will deal the normal quantity of damage, but damage dealt will not heal by any means until the weapon is broken.