Bear in mind that the HK Airport Express includes free bus transfer from (and to, when arriving into HK) most higher-end hotels. I would think it would also be possible to walk from a low-end hotel to a nearby higher-end hotel and ask the staff there where to wait for the AE shuttle.
See details
here.
I have found this very efficient every time I have used it; few minutes' wait for the bus at my hotel, staff load your luggage, at the other end you are near the AE checkin desks, check in bags, proceed to AE station and on to airport (or elsewhere then to airport, if one wishes). I could only dream of such a service with the Heathrow Express.