From ERL at Bandar Tasik Selatan to Putrajaya ERL is only cost RM 5.?0 and it took 25minit.
Go out from the train and purchase another ticket to go KLIA which is only cost RM?.?? (i think is RM7 if not mistaken) which I can remember and it took abot half and hours.

But if you are from Bandar Tasik Selatan straight until KLIA, it will cost you more than RM 5.?0+RM?.??.

But if you will like to save cost then you must spend extra half an hour at putrajaya station. For me it is worth to spend extra half an hour because for not mistake I can save about RM5.

You can always take KTM from KL sentral to Bandar Tasik selatan for only RM1