What is the value of an old King Manufacturing BB gun?

Whenever you have an antique, the value is determined by the condition of the Item. If I asked you "How much is my 57 chevy worth?" You would ask "What condition is it in." It's the same with air guns / rifles.

You need to provide more information. Give it some sort of rating like. POOR, FAIR, GOOD, VERY GOOD, or ExcelLENT. this will help me set an estimated value.

Your asking about a BB gun. Are you sure it's not a rifle. As far as I know King never made a BB gun only rifles. Be as clear with your question as possible and I will try to answer you. In fact, which model are you asking about. King made several different models.