Suggest Treatment For Severe Acne

My son has a bad acne problem and in the past has been prescibed a clindamycin / benzoil peroxide mixture. When we've recently tried to get that filled it's either on back order or would cost over $100 for a one month supply. Is there something over the counter that would work almost as well. We've tried most of the topical solution which work great for a week or so but then the acne always comes back just as bad as before.