Why is PHP better than ASP?
No windows license required – run it on your Linux server.
Technically you don’t have to buy an IDE to code ASP, however most people do. PHP editors ideally are just a text editor with syntax highlighting, however with eclipse you can still have a free, fully featured IDE for PHP.
Apache/PHP uses dramatically less resources than IIS/ASP – so you could get away with cheaper /older hardware. Works great with Linux.
Generally speaking Apache/PHP is significantly more stable than IIS/ASP, so you will have generally better uptime.
PHP.net has great documentation for hard-core developers, all the way down to the I just started today developers.