It used to be common knowledge that an infant in lap was always free. However recently I have heard, (and confirmed on Delta) that an infant in lap, at least in F/C, can cost a few hundred dollars. I've heard anywhere from $200 to 20% of the would-be fare, which on a $4,500 F/C ticket booked with miles, 20% is $900.
Can anyone state their experience with IiL (Infants in Laps - my own term)?