Replace radiator cost?

What is your question?

I just purchased a 2000 Monte carlo and its been over heating as soon as I get in the car. I had a friend look at it and he said that there is STOP LEAK inside of my radiator which is causing it to be stopped up. Its preventing the flow of the fluids which is making my car over heat.. I need to know the cost of the repairs and if it would be best to just replace the radiator?