well PHP is open source and free:
http://php.net/ It can be installed with IIS (windows web server) or Apache. It does however need to be configured on the web server itself.
Do they use any server-side programming language? I understand about being polite, but it's probably also in their best interest to consider such technology. It will help in terms of development efficiency and allow them to do a lot more with web applications.
I don't know if you code outside of work, but it would definately be worth installing and playing around with it on your local pc to see what kind of power it gives you.