The cost of not treating
The cost comparison is not subtle. Community-based outpatient mental health treatment costs $4,500 per person per year. Incarcerating someone in a state prison costs $85,000 per year — nearly 19 times as much.
Emergency room psychiatric boarding costs $2,200 per day. Many patients board for days or weeks waiting for a psychiatric bed that doesn't exist. Annualized, this is the most expensive option in the system at over $800,000.
The spending inversion
Federal and state spending on criminal justice for people with SMI exceeds $15 billion annually. Federal community mental health spending is approximately $5.5 billion. The system spends roughly 3 times more to incarcerate people with mental illness than to treat them.
This is not an argument for any particular policy. It is arithmetic. The cheapest intervention is treatment. The most expensive is its absence.