Understanding the cost structure

For an organization - are users multiplied per workspace (i.e. if we have 20 users is it 20 * (#of workspaces) * $79/mo)?

Users are per account which contains all workspaces in that account.

If you have 20 users, they are 20 users for the entirety of the account, with access to n number of workspaces within that account (with the restriction of RBAC permissions they have in each workspace).