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 you hire a professional web developer to make a website for you, it is also going to cost way more money. There are low-priced developers, and then there are high-priced developers. But no matter what you are going to end up paying way more than what you expect. Each one comes with pros and cons. Low-priced website designers are not going to be that experienced, but that is why their prices are going to be so low. This does not mean that they do not have the skills; they just are not proven enough yet to warrant a high price.