I think many people get confused about; not buying excursions from Carnival. I've never purchased an excursion on my own where I wasn't a part of a bigger group that purchased theirs from Carnival.
You have to look at it like buying apples from an apple farmer. If I lived across the street from the apple farm, why would I go to the supermarket to buy the same apples? The supermarket (Carnival), is going to mark up the price of the apples from the farm (The Tour Vendor), because they have to make money for getting that product to you but when I get off the boat (my front porch), and walk 100 feet to the gate (the farm), the apple (the excursion), is still the same, except cheaper..
All my neighbors will be there with their higher priced apples and I'll be there too.. With my apples that are just as red, just as juicy!