Actually, if you buy the skyray kit you get all the bits you need to make any of the three. They include the hammerhead sprue in the skyray box because there are components on it you need for the skyray as well. The skyray is only $5 more and comes with all those bits.
Buy a devilfish?
Pretty bad advice. He wants a devilfish with a smart missile system, there is no
SMS in the devilfish kit as it's on the hammerhead sprue. Buying the skyray kit is the best deal as he'll get both the fish and
SMS and all the extra bits as well.