Probably too late for you now... but for those who can book a reasonable time ahead ... it is so chaep that one can buy two or three tickets spread over a number of days to travel by budget air line air asia from Johore Bahru to Penang on Air Asia - and similarly hop on the one that suits you on the day. -- just throw away the other two tickets. I have done this personally - and it works fine...much cheaper than surface travel and quick, just a minor effort to get across the causeway into malaysia - but that ain't hard.