To give a group of people, such as staff, a discounted rate for an event ticket, you must create a separate fee with the discounted rate, which can be seen by anyone using the registration form. If you don't want everyone to see the discounted rate for staff, you must create a separate registration form that has the discounted rate that will just be shared with staff. Adding a promo/discount code option in the registration form would allow organizations to offer discounts without having to do extra work (create additional fees for registration forms or additional registration forms).