The newest studio runs on the Eclipse platform. It's got Zend Framework integrated directly into it for type hinting.
I think it's worth the $200; however, Aptana seems to be a less-costly alternative to Zend Studio and is built upon Eclipse as well.
Most good IDEs will automatically do everything you described. Even some text editors (Notepad++, EditPlus) will do syntax highlighting and if given proper code, some code insight 😉
There are other good IDEs including NuSphere PhpIDE, ActiveState Komodo, MPSOFTWARE's PHPDesigner, Waterproof's PHPEdit, and Blumental's WeBuilder 2008 or RapidPHP 2008.