Adult or not, I know how hard it is to sit around watching someone you love dearly flounder and barely keep his head above water.

Maybe it's not the "right" answer from a logical perspective, but I would do everything in my power to help. But, it would be in the form of getting him to a specialist.

My husband, at age 32, is now seeing an ADHD coach, and she is extremely understanding about the common struggles that ADHD/ADD adults face. Although several years ago, my husband was extremely resistant to the idea of meds or therapy, he now has a much better perspective on how the coach can help him. He is a competitive athlete and it is common to hire coaches for THAT, and he sees the ADD coach much the same way -- to help him improve his performance with techniques and strategies.

I really hope that your son can learn to manage his cash flow, for both of your sakes. You sound like a terrific parent.