When the radiator has failed, either through leaking or from clogging up, replacement must be performed right away. Severe overheating causes catastrophic damage to an engine, and leads to much bigger and more expensive repairs.
Most repair facilities will be able to change the radiator, and usually can do it in the same day, with radiators running between $120 to $300, depending upon the type of vehicle. Installation can cost an additional $100 to $300, based on how much labor time is involved to change it.
Upper and lower radiator hoses are a good add-on during the repair with very little or no additional labor.