I've never known anyone be charged for checking in their car seats , if you take a black plastic sack just to protect the and make sure they are well labelled. I would recommend you keep the buggy with you (as long as it's not one of these HUGE ones and then you can use it at the airport whilst you are waiting, they will take it off you as you board and store it with oversize hand luggage so you don't have to wait for the checked luggage before you get your buggy back.