Amazing amount of scratches have little effect on the image. HOWEVER, fungus is a major problem not because little will affect the image but it will spread if not cleaned properly.
I had an enlarger lens that had a good amount of fungus. It has eaten into the coating and in process of cleaning it, major part of it flaked right off. In other experience, just a light fungus cleaned off by simply wiping it with regular lens cleaner. I don't know how much money you are talking about but you really won't know if it will clean acceptably until you try it.
I wouldn't purchase a lens (or a camera with lens) with fungus. If you want a dreamy image, you could use a filter.