If some one is that good you'll have to pay them well to keep them around.
If they feel they are being taken advantage of they'll be gone.
From what it sounds like I would say that he should be in the $15 to $18 range.
Let him know that advancement is there should he continue to be a productive worker.
Professionals are people who can do their job when they don't feel like it.
Amateurs are people that can't do their job even when they do feel like it.