The discovery phase of a project is important. It's necessary to explore ideas, identify core functionality and clearly document requirements. It's also a time when you discover things that can absolutely not be accomplished given the tools and time available. This directly shapes the minimum viable product and provides a clear roadmap for how to proceed when it's time to start developing.
Skipping, or cutting short this phase of a project, should never be seen as a way to trim cost. In fact, taking such an approach will most likely have the opposite effect. I've seen it happen and its not fun for anyone involved. No project will ever be perfect, but you can do yourself a big favor by not scrapping this critical step.