Is $7,000 to finish my bathroom a fair price?

I had a 3-month long project with a contractor to finish my bathroom, which was the last item on my punch list before listing my property for sale. The original agreement was for the work to be completed in a week for $7,000. The contractor repeatedly delayed the project, and near the end, with the work only 90% done, he demanded an additional $7,500 for "added items" that were not clearly communicated or priced. I believe many of these items should have been included in the original contract. I attempted to negotiate, offering to split the disputed amount, but the contractor refused and threatened to file a lien. Legal advice indicated that pursuing the matter in court would cost more in attorney fees than the disputed amount. I feel powerless in this situation and am seeking advice on how to protect myself from similar issues in the future.