The important consideration in Discovery is to understand the overall cost picture. It is important to know what the cost components will be, how they interact with each other, and at least a ballpark idea of how much money you're talking about. The team should think about what factors might cause the costs to change over time and how dramatic these changes might be. The team should also think about funding options and discuss possible impacts and issues relating to the funding options. As projects move from Discovery to Delivery and eventually into Service, the need and purpose for the business model will change.
Business models evolve just as projects evolve.
For example, a business model begun in Discovery can evolve into a budget, rate model, or a combination of the two as the project transitions through Delivery and onward. As it transitions, it becomes increasingly more important to get accurate costs. Generally, this is about the time when the design details of the project become clearer and cost estimates are more easily obtained. Thus, a business model is not created just for Discovery or just for Delivery and so on. A model is created that is developed and refined as the project makes its way through its lifecycle.