Make webite so subdomain is imbedded in title, meta and headings and content. More explained bleow with example

This is a subcontract job, I am making a website for a client, but they want to be able to have it so te subdomain dictates the SEo to some extent. I had not seen this before not sure how to do it. For example [login to view URL] if you click you can see the keyword benfleet in the title tag, meta tag, and in the body and heading for the web page. If you instead enter [login to view URL] it refers to Basildon. But these are not static HTML pages because if you type in [login to view URL] You can see the word anythingatall is used and so on. So there must be a way to make the subdomain name be imbedded in the heading, keywords and the content, and its that I need doing. I have nto yet started to build the site, the winning quote will get full access inc ftp and phpmyadmin, but first i need to know what you need me to build it in (for example, is this a Joomla plugin?) The project is to do the coding aspect I can put together the site and the hosting.