I recommend you contact your state attourney general. Many states have rules about estimates, repairs, and exceeding estimates. Filing a complaint with the BBB can also help get some action from the business in question, because they will have to respond in order to get it off their record with the BBB. I have found the AG to be most helpful, and businesses are quick to respond when they get a call from the AGs office. If they have violated any state laws, they could be in serious trouble.
I certainly hope our members can give you some ideas of how to resolve your complaint. Feel free to discuss your situation, but please do not name the vendor publicly. That would violate our Community Policies.