Of course, this is only a ballpark figure and the final rate will depend on a number of other factors. For example, if the proofreader needs to cross-check the index, this would naturally escalate the cost. In non-publishing industries, costs may also vary. A proofreader with a deep background in technical writing may choose to charge extra for their expertise and fact-checking, for example. But whatever the cost, you can be sure that getting a professional proofreader is worth it.