I know nothing about vintage bmx bikes, I'm into the old balloon tire tank bikes. But I have a guy offering to trade me this 1981 Mongoose Supergoose for some Schwinn B6 parts. I would likely resell this if I do the trade, but don't have the slightest idea what this thing is worth. I know some vintage bmx are valuable and others aren't, but they all look about the same to me. Please help! Below are the pics he sent, and I would be getting the complete bike as shown. The frame pics are when he had it apart to clean it up.