The Sea Sparrow issue wasn't expense or room. Iowas have plenty of room.
It was the overpressure when the 16-inch guns were fired. The Sea Sparrow box launchers - Mk. 29 I think? - just weren't able to take it.
I know that. I was thinking of the Des Moines class when I said that. You'd also have to fit SPG-62 or SPS-65 fire control radars for them, too, thus also further taxing the ship's electrical supply. I don't know why one couldn't have made mounts for the Mk.25 and/or Mk.29 that retracted into a box when not needed. When you need the system, it pops out of its box, shoots and then drops back into its box.