Here we consider such a use case. The cost of the project determines the cost of the project for the customer (client). In a budget, you determine the amount you want to spend on the project as a contractor. If you set the cost of the project to, for example, 2000, then define the budget as 1000. This way you will define a guaranteed profit of 1000. Please take a look of the below 2 picture references to make the situation clear.
- this one
- and this one too