The rulebook is $20. You probably were looking at a chapter specific racial packet for $5.99
Membership is chapter specific. It depends on what chapters you are planning on attending.
The next event depends on which chapters you plan on attending. There is an HQ and San Francisco event June 3rd. http://www.alliancelarp.com/calendar.php <---- this is the event calendar
Membership
Membership costs are determined locally. There is no national membership fee.
Events
Again, this is entirely local. Alliance has many chapters across North America and each Chapter has its own schedule of events. Find your nearest chapter here.