Website QA testing is a process, which is integrated as part of the web development process and you don’t need to pay separately.
Website QA testing for existing websites is a web service, that is usually needed for existing websites, which are slow or not working properly and some tests should be made, to find the current status of the software and make a list for bug-fixing.
Usually the QA testing is needed for websites, developed by another web agencies and web studios, which ask for more money and the result is still a buggy software.