You can define Prices (Billing Rate, Cost Rate) for Resources. Here you define the prices for each resource with optional overwrite per Account, Project, etc. - check details.
Often, project pricing is based on Roles (e.g. Junior, Senior, Manager, ...). This allows for maintaining generic role rates rather than individual rates. The role rates are used if no resource-specific rate is found.
Once set up, you can use the Rate Management page to easily view, create, and maintain resource prices easily.
in Setup > Picklist Value Set edit Resource Roles
Add the names of the roles you are using.
For the individual Resource, select the typical Role in a project, etc.
If a user provides multiple roles in different projects, just specify the rate for the exceptional project directly.
If a user provides multiple roles in a project, use the Activity Type to overwrite the rate.
If you want to add role-based prices manually, search for the 'SystemResource' and add the prices with Role to that placeholder Resource. For a better user interface, use Rate Management.
When you select a Role in the Resource Price, technically the resource is assigned to a 'SystemResource'. If you delete the System Resource, you delete all Role Prices.
Note, that if you select a Role in the Resource Price Tab for a 'normal' resource, note that it will be saved - but for the System Resource (i.e. not visible in the Resource Price for a normal resource).