We cannot quote a figure here. Because the cost of your email hosting solution varies depending upon the plan you have chosen. As is always the case, the more you pay, the more features you can access.
Because a lot of service providers (e.g. Gmail, Rediffmail and Yahoo) offer free email services, email hosting can be costly. But a paid service understandably offers superior features that streamline and secure your communication. Besides, a corporate email reflects your business in a positive light and adds credibility to your message.