More GameObjects or sin/cos calculations, which is faster?

I have around 300-500 enemies that can be active at a given time. Each enemy has needs to know the spawn point for its bullet. They also have multiple spawn points based on the type of attack. What would be faster (as in more optimized): Placing "spawn" empty children into each enemy which acts as the spawn point, or to have it calculate the spawn point for every bullet fire? I ask due to the amount of GameObjects this would create.

EDIT: On a side question, does anyone know if a box trigger...

More GameObjects or sin/cos calculations, which is faster?