If you purchase a SDC season pass, the Branson Belle's lunch cruise is half price. I believe the dinner cruise is a 10% discount with a SDC season pass.
If you plan on going out to SDC more than one day, the season pass seems to be the most economical way to go.
Personally, I thought the Branson Belle's lunch cruise was a pretty good bargain. It was the same show as the dinner cruise but, the headliner wasn't a nationally known act. Everything else including the meal was the same. The food is average at best but decent. The entertainment was very good IMO and it was an enjoyable afternoon and evening. If we ever go again we'll probably be happy with the lunch cruise.