I assume you are originating in KUL. As you would ONLY have access to the domestic airside part of the terminal, you will have zero options to sleep airside (apart from perhaps benches!) and the domestic MH lounge will close close to or at midnight before opening again at around 5 or 530am.

So your options are just landside hotels - the cheaper ones are at KLIA2 area (Tune Hotel, Aerotel, etc) a train ride away.