As an administrator, you can assign the View Cost Analysis permission. When enabled, this permission allows a user, who is also a stakeholder but not an administrator, to set the timeframe on a process activity and contribute to the cost estimate including adding materials.
Steps to set up the permission
From the Settings menu
Select the Users button
Select the appropriate user
Open the user detail screen, and select / unselect the View Cost Analysis permission
Administrators can apply permissions in bulk
Timeframe costs can be analysed in the time & cost analysis report from the sidebar, and are aggregated in a timeline on the process map when Display embedded view is checked (embedded roles).