Basic membership in the SCCA is $55/year plus the cost of any Regional Dues; typical regional dues are $15, and some are slightly higher. Spouse memberships and Family memberships are available. Membership applications should be obtained from and sent to the National Office (the maintainer of this unofficial web page is not empowered to deal with any membership related issues.)
A temporary membership is available from many regions; it is good for six months and allows the temporary member to work at races and participate in many types of events (although it may not be used when obtaining a Competition License.) It typically costs from $15 to $25; the actual figure is determined by the SCCA Region.
One of the major benefits of SCCA membership is a very good insurance policy. Coverage is three-tiered: non-members who sign the insurance waiver forms are covered at the lowest level, members who do not hold SCCA licenses are covered at the second level, and members who hold SCCA licenses are covered at the top level. Thus, it is in the best interests of any SCCA member to obtain some sort of license. If nothing else, check off the "Crew License" box on the membership renewal form -- it's free, and it gets the job done.