Details on the HKAOA website under the "join" tab.
Of particular note for you are the fact that no back payments are req'd for previous members and the discount scheme already in place for new joiners:
6.5. Any officer who applies for initial HKAOA membership within one year of becoming eligible for
membership will pay an introductory reduced subscription rate of one half of the Full Member
subscription rate for the first 12 months of membership.
6.6. Second Officers and Freighter First Officers applying for membership under the terms of the
preceding paragraph will enjoy the reduced subscription rate of one half of the Full Members’
rate for the duration of their time in that rank.
Any more excuses for not joining?
I've read all the stuff about what the AOA may or may not have done for us over the years but the fact remains that they are the only people trying to improve our pay and conditions, or maybe resist the erosion of them would be more accurate.