I am just starting up a campaign and a player wants a Innate attack that manifests in different ways. The genre of the attack is believable for the setting however I do not know how to charge him for it. I would love some sugesstions.

A close example would be having a flaming/burning innate attack able to manifest as a jet stream of fire or as fireballs each with their own moddifiers to the innate attack rules. Should I charge him for each way it manifests, or should I just combine all the multipliers for a final total? Just a pair of options and am open to other ideas as well