We might divide a page template into a header, content, sidebar and footer where these are in separate files. The content will change most between pages, so rather than having a content file, we include the content into a page file which pulls in the individual template files and defines the unique features of that page. The unique features of a page will be the title, description and article content. We can define these at the start of the page template with say PHP code to set the value of variables that are used by the other templates such as the header template. Then we assemble the page by including the required templates and inserting the content.
When it comes to the high-priced website developers, they are going to have a reputation to back them. They are going to have a portfolio of professional websites they have created that are going to speak for their work. High-priced website designers are going to have people who could vouch for them as well as have a very strong web presence. This is the reason why they are going to be priced so expensively, because what you are really paying for is a degree of certainty, not necessarily superior quality.