Delsym is one of the brand names for dextromethorphan. In the United States, it might cost around $15 for 90 milliliters. Robitussin, another brand name for dextromethorphan, might also cost around the same amount.  There are also generic formulations sold in many pharmacies that can be cheaper. When looking for generic forms, check the active ingredient to make sure you are purchasing the correct medication.