of bim courses on revit there is a wide offer on the web with very different prices one from the other and I understand that it is difficult to understand which to choose.
I think you could start with a basic course of a few hundred euros and a few dozen hours to learn the first rudiments. After working on it for a while, your projects will suffer from some of your training deficiencies and, in this case, you can choose a more detailed course based on your actual needs.