asking professor to fund Master's student
You might be mistaken about your professor having funding in abundance. Even if he has managed to bring in a lot of funding, he might be spending it all on research and researchers.

One possible way to address this might be to approach your professor at an appropriate time and gently bring up the possibility of receiving funding for your work. I would even leave it up to him how many hours per week should be paid.

As a matter of fact, you might mention immediately that you also keep working if there is no pay. It might seem that you will not receive anything when you mention this, but your professor might feel that it is morally right to provide some funding, and it will make the conversation less awkward.