Rathergood
I have hesitated reply for someone to give you a direct answer. I am by no means an expert on tv repair, but I had a close friend who worked with me fixing tvs. If my memory is correct the issue you describe is caused by the green picture tube shorting out. It draws more juce and creates the green screen by causing too little voltage for the two good tubes. Wether or not just changing the one tube will fix your set, I do not know. If you take it to a tv shop for repair it will sure be $250-$400. Most repair shops will give you an estimate for $50 or so. But if you do not want to put much money in it. The money paid for an estimate could be part of payment for a new set.