Slack has raised our charges by $195k per year

Almost certainly an organizational failure. Salesforce, despite its many faults, has had good non profit programs for many years. They also tend to have procedures about notification for renewals and account managers to discuss terms and the like. Some automated process or internal person with enough context made a mistake. A jump like that should have required direct outreach and phone call to see what can be discussed. It doesn't seem like saleforce has some kind of policy shift to charge maximum rates to non profits. Elsewhere in this thread it seems like this organization had some kind of special one-off deal to handle the case they had a number number of non-employee users. The slack billing model doesn't seem to work for "communities" but if they agreed to such a special deal they shouldn't just suddenly drop it with limited notice. Thus my contention is the specifics of the special deal where lost in some form of automation or lower-level employees actions following a standard playbook.