CMS helps to separate design of web site from its content. It means designer develops a web site and gives it to its owner or manager who can fill a certain design with different content. If necessary the content of web site, its images and graphics can be easily edited without intervention into design of web site. All changes become visible as soon as you make them. (Don‘t forget to reload page after making changes). Even if you are not an expert of HTML coding, you can easily manage the content of your web site yourself.
With website templates you can get the best of both worlds. You can get something that is low-priced, was made by a professional developer, and is going to have at least a semi-professional look that should suit you just fine. These designs have been developed exclusively for professionals and individuals who want a simple solution. You will be able to add your own images, content, etc. to the site. As far as price goes though, it can definitely fluctuate. You can find low-priced templates or higher priced website templates.