In the world of an ever-changing market, you want to make sure you're designing your product that has a market fitment. You’re not sure about how it will shape up and which will be a key requirement or priority features. If this is the case, then a fixed priced contract is not the right choice as requirements will be fluid and changing. You also want to have a flexibility to directly "driving" the scrum team that can be dynamically optimized based on your needs. Techify has an option for you - Time and Material based option with Agile Methodology.
Every sprint of the agile life cycle is defined based on mutual agreement between client and developer to shape up the product you envisioned. Each sprint has defined delivery that will also help you envision your product grow from scratch to mature level.