Ether

If the spell that's copied has an X whose value was determined as it was cast, the copy will have the same value of X.

After Ether's ability resolves, the next instant or sorcery spell you cast that turn will be copied whether or not it has targets and whether or not you spent the mana added by Ether's ability on that spell.

You can't choose to pay any additional costs for the copy. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.