User wants the vendors to be able to see what they are owed in CORE. The vendors are added as CORE users with the Time & Expense security profile. However, they also need to have the right subscription that allows them to access the Time & Expense features in CORE. Please check with your Sales Account Manager to purchase the required subscriptions.
With the right subscription and security permissions, the vendors can see the rates that they are getting paid at by exposing the Cost Rate column in the Time Entries and Expense Entries screens (More > Show/Hide Columns > Cost Rate). Check CORE Help Center for details. Additionally, they can see the cost rates by running the Time Details or Expense Details reports. Check CORE Help Center for details on running reports.