OP here, bad news. Went and saw it today, and it is black mold top to bottom. DH, a contractor, says its even into the wood foundation. Because of my severe allergies, the only way he'd even consider it is if we did a total gut and basically put a whole new house on it. Whoever did the appraisal should be ashamed of themselves, it's not safe to live in, in the condition it's in. We could offer what the land/garage/septic/well are worth, but just aren't sure we want the hassle.
Thanks for all the advice, though, it was really great!
Terri