If you need to run a web site with database interaction or e-commerce, then it is time to consider dynamic web contents.
PHP is free
The LAMP (Linux/Apache/MySQL/PHP) runs on cheap low end hardware and this means by purchasing a cheap hardware running on Linux OS, you basically pay nothing other than the hardware cost as all the listed above is FREE!
PHP is easy
PHP does not require a deep understanding of a major programming language. It's easy to learn and the available support has always been about individuals banding together to create resources for one another.
PHP is cross platform
PHP runs on most platforms. The native platforms are Unix (including most flavours like Mac OS) and Windows.
PHP is stable
Stable means the server doesn't need to be rebooted often and PHP doesn't change radically and incompatibly from release to release.
PHP is open source
PHP source code is freely available, a community of developers is always working to improve, add to and find bugs in the language.