The amount you should charge for making 40-50 backlinks per day depends on several factors. These include the quality of the backlinks, the niche, and the time required to create them. If you're offering high-quality backlinks from reputable websites, you can charge more. For example, you might charge anywhere from $100 to $500 per day, depending on the difficulty of obtaining the backlinks and the value they provide to the client. If the backlinks are lower quality or automated, you may need to charge less. Always ensure the backlinks are ethical and comply with Google’s guidelines.