Eden,
First, Welcome!!
I have a 30 year old alcoholic son and he just did get out of jail. It has been my experience that when I stopped helping him he found someone else to do it. When he was being released I told him he could not come here and he was very close to been relesed to a half-way house or a shelter when a friend stepped in.
Look at it this way. Has one thing you have done for him in the past changed where he is today? No? I thought not. So it only seems reasonable that there is nothing you can do today that will change tomorrow for him.
There are free rehabs like the Salvation Army, AA is donation (usually a buck) each meeting, and many other affordable resources out there if he really wants them. One thing I have offered my son is the 1st month of a halfway house or any other program like that. I won't pay the whole freight but I would help him get a leg up.
Come on down to the Al Anon (Family and Friends) forum...there are plenty of parents in the same boat as you. We paddle along together...
Hugs,
JT