I know Carnival, Celebrity, NCL, and even Disney do not provide formula or baby food. I was surprised about Disney but even they have a contract partnership where they will sell you baby food and supplies as does RCI.
As for the cruise fare - some lines have kids sail free at certain times of the year. But it is a promotion and not a standard thing. Costa does it fairly commonly though.
As to the food - there are so many variables with babies that a cruise ship would have to stock dozens of different brands, blends, etc., in order to address individual preferences. Babies are a lot like cats when it comes to eating. Baby #1 only will eat Beechnut strained pears. Baby #2 wants the Gerbers pears.
To be honest, cruise lines tolerate infants but do not court them. RCI does have their Royal Babies program where they can have some activities, but a parent has to be there. I believe there are also limits on the number of infants that can be aboard any particular cruise.