Setup Concrete5; it's incredibly expandable with all manner of great features and very easy to use and update.
It requires mysql, php and apache. Very easy to install. Seriously - I have a couple of sites setup using it:
You can set permissions for public content, private content, guest content, group content for forums, picture sharing, calenders, and use Google widgets, mailing lists, and more.
All basic features are free; you can expand with various commercial offerings including an eCommerce store (for additional $) all with a couple of clicks from their dashboard.
Set it up and see how much easier than any other CMS this is!