I'm a 20 year old student studying Graphic Design. I occasionally get clients who would like me to completely redo their website such as designing a custom theme, adding plugins and doing it all with wordpress.
This depends on who your client is, how much their revenue is, if the website will give them a ROI (return on investment), and how talented you are.
My agency (https://www.brotskydesigns.com) does pricing based on what we estimate the time commitment will be. If we estimate the job will take 40 hours and our hourly rate is $x we simply charge $x * 40. We make sure to cap off the hours so clients don't take advantage of us and we don't end up stuck in endless projects.