No pre-requisites required for Andrew Ng ML course. There are a couple of lectures in which he gives basic idea of Linear algebra. Also you can learn math when required.
Andrew Ng's course remains a top-ranked machine learning course because of its unique way of teaching. This course is blended with many standardized learning opportunities provided by Stanford University. If the question is about what you pay worth, you need to consider the course from below to aspects.
If you are interested in machine learning (you should) and you are a beginner or know very little about it, Andrew's course is the best investment of your time that you can make.
To get started with Machine Learning you must be familiar with the following concepts:Statistics.Linear Algebra.Calculus.Probability.Programming Languages.