RCI doesn't have an early saver bookings. They do have savings certificates you can get by signing up for e-mail delivery.
Once you have cruised with them and are in the Crown & Anchor Society you have member access to other savings certificates.
Go to the RCI website and along the top there is a pulldown menu for 'cruise deals' which has several options to look at. An agent can get those prices and perks too, so it doesn't have to be booked direct with the line.