Like for any other plugin, in order to modify permissions for Budgets, you should go to Administration ---> Roles and permissions. Click on a role you would like to modify, and then scroll down to the Budgets section. Enable or Disable the appropriate fields:
Budgets
- View project billing details
- View issue billing details
- Manage project billing details
- Manage issue billing details
Please check the below screenshot reference to make the situation more clear:
