This is a difficult question to answer. Try to avoid saying a number right away. In the work place - you want as much as possible and the company wants to pay as little as possible. So you need to be careful how you approach this question.

You may want to research the market place to find out what the average pay is for this kind of job.

You may say that, with your background and experience you are worth between R? and R? per month. Or, you could just say that you're more interested in what this position could do for your career.