Status update:
We're a little closer now. They've agreed to most of the electric demands on the Addendum. The rest of the stuff we've just written off. I can put in some PVC myself, and the other stuff is minor.
Right now I'm researching the Aluminum wiring issue. The local Fire Inspector says that the homes around here are relatively well-constructed from an electrical standpoint, and they haven't gotten any calls that were caused by bad aluminum wiring jobs. As long as the Al in this house is installed properly, it shouldn't be a concern. The seller has agreed to have a licensed electrician replace the breaker panel, install some GFI outlets, and fix the bodged electric jobs that the previous owner did. It's looking good for this one!