I think he's probably going to have to wait until the free program has an opening. But he should check with the lawyer who handled his plea. The lawyer will know all of the facts of the case, the predisposition of the judge and DA involved and will be the in the best position to assess your brother's chances at a sentencing modification. He might also know of other programs that are in your price range.
I would contact the attorney who handled the case. If residential treatment was the negotiated disposition, it may be dificult to modify it to out patient. There are some programs that will accept a resident if the family can assist financially for a short period of time. You may want to consider this option. Unfortunately, the waiting list time is not unusual.
It is also important to note that if your brother is unable to attend because of financial issues there MAY be an equal protection argument that would preclude the court from incarcerating him for his failure to attend. This would be a very fact intensive analysis that would require the assistance of a local attorney.