dandruff?

This is sort of a random post... But my man has such an issue with dandruff. I've never had the issue so idk how to help him but he's tried like everything. Head and shoulders is awful, selsun blue is literally the worst shampoo in existence... Right now he's using this loreal stuff that actually has helped a little bit but it's still kinda there. I know it makes him self conscious... Is there something I could get him that won't cost like 30 dollars a bottle? Lol