Assembly dues are set in the By-Laws and by Supreme. There are three classes of members along with their dues: Regular ($30), Honorary Life ($10) and Life ($0). Dues for Regular members are set by the assembly and documented in the By-Laws; dues for the other classes are set by Supreme.
To pay your dues online, click on the member class you are below. (Hint: there is only one Honorary Life member so chances are it isn't you.)