Fill the project budget with planned expenses on project management, hardware and software procurement, etc. Project workloads will be calculated automatically based on the employee rates and estimations of the tasks assigned to them. The more detailed and complete the structure of project works is, the more accurate is the budget estimation for the whole project.
If you don't know the particular assignees, you can use the following technique for estimation of costs of potential projects or requests for proposal. Create dummy accounts for the required project roles. Use average cost of an hour of work for rates of such "employees". Assign tasks to dummy "employees” to estimate the planned project budget.
If the project is started, you can easily replace dummy "employees" with real ones by means of bulk operations, balance their workload, and get the more realistic project deadlines and budget.