You just "pay up" for each individual Games that you want to throw at, though how it works outside the US West Coast, I'm not sure. Around here, SHA "members" are just the guys who throw a lot and help out. We all pony up for each Game, individudally, there is no actual "mebmership". Ditto for the SAAA, I believe.

Joining NASGA is literally filling out an online form which gives you access to post to the database and the forum, that's about it.