Hello! We can tell you more about what contracts you can choose to estimate the cost of an application
The advantage of a fixed-price contract is that it defines the amount of work that the company has to do for a set budget. In this case, the client gets the full cost of the project.
In a Time and Material contract, the client is billed for the actual amount of work done by the developers, based on a daily or hourly rate, regardless of the stage of development.
For you to choose the method that is right for your situation. Study the pros and cons of each contract and decide which one is right for you. If working on a fixed-price contract is not right for you, a fixed time and material contract is the best option for such cases.

You can find out more about an app cost estimation in this article, which details everything