Kaffe and Tula do "require" a higher thread count fabric. Lori Holt and Tim Holtz don't. In my area, Kaffe and Tula are higher priced than Lori Holt and Tim Holtz. But Lori Holt requires a lot more fabric for her sew-alongs, than what is needed. For example, you may only need a 2 1/2" square, but her kit gives you a whole fat quarter.
It's been my experience that when people are a fan of a certain designer, they will pay the price.