Good morning, Hummingbird!
I can only speak to what we did. The late Mr. Seren maintained the payments for his son's health insurance, even when his son was not working. So, that covered more than half of the payments for the rehab. Mr. Seren had a job that made sufficient money for us to cover the remainder.
The only time my stepson decided rehab was OK was during one of his hospital detox stays, and Mr. Seren was assisted by the social worker at the hospital.
At that time, my stepson was living with friends - so no apartment to deal with.
We have never hired an interventionist.
He went to sober living for a while after rehab, and paid for that out of the income from the job he got soon after rehab.
All of this while we were living a 9-hour drive away....