It will often vary by location. Some specialty classes can draw a little more money. Typically the government such as the military will set a pay grade. Usually a university, city, or community center will pay around the same, often $15-30 per hour. Others you must treat as though they are clients and name your own price. If I need to pay an independent contractor, I look at what others pay in the area and set a fair, non-negotiable price, sometimes based on their qualifications as well.