Its upto your sponsor , what commission he take. The usual rates as of Buisness Visa Now is QAR 300 per month . You can check with any travel agency. That is QAR 100 extra commission for every month of stay.

The rate of QAR 2000 for 3 Months existed in 2011. You are going back in time.

However if the renewal for 3 months is after the first 3 Months, then the charges are correct somewhat. Because usually the maximum period of business visa is a 3 months period. Further renewal need special approval and agencies charge 1000 riyal for the renew approval itself.

To summarize:
First 3 months : 900 Riyal
Next 3 Months: 1000 Riyal + 900 Riyal