I can't help Kowloon side, but I agree with tentseller and christep.
Hong Kong has a lot, and I mean A LOT, of laundry places. They should charge by the KG or maybe the pound.
I can't really help with any specifics but...
I've seen some on the Southern end of Nathan Road before - which is probably easier than hulking a big bag of dirty laundry across the harbour.