I recently had a contractor complete some landscape. He had left out some additional work from the original bid. I need some rock placed in a ditch to prevent erosion. He quoted me a couple of hundred dollars, with no official bid sent as he had done with the original project. I got a bill in the mail for $2500! He says that he can reduce it to $2000. I would have never agreed on a project with such a price tag. How do I dispute this?