Not the worst idea, probably run about a grand from what I've heard. If he isn't mandated to have it though he will probably just get it removed or find a different vehicle. You are treating the symptoms and not the causes. He needs to come to a realization that it is a problem first then have a support system to help if he isn't capable of change on his own.
If you want to force the issue notify the police when you know he is driving drunk.