Rock,
Where does the $10.00 a day come from? If from you, what do you get in return for that $300+ a month? If you are not getting paid back, why do you believe that you owe him that money?
Your son may not be able to "get a job" but he could apply each morning (in my town at 6:00 a.m.) for daily labor.
My brother is in the same place as your son, has been for years: though he has a military disability,it does not cover the basics that he needs to live, and he can't get or hold a full-time job.
I am sorry about this. But I hold down two jobs and have trouble making ends meet. I tell my brother that his JOB right now is to show up for manual labor each morning at 6:00 a.m. If he will do this each and every morning, then I will listen to his problems...but I don't want to hear about them if he is sleeping in until noon.