He sounds a lot like my Teddy in personality, only Teddy was already trained, just very worried and anxious about everything. I have personally found it SO rewarding to get him to where he could trust someone again. Watching him come alive little by little. And the day my daughter rode him in a lesson and you could see how hard it was for him because he was still anxious and she had never really ridden him, but he tried SO hard and he did SO well.
When I got him, I swear he had the exact same look in his eye that you're describing: "I'm worried about this. Can I trust you? Will you treat me right?" If you have experience training a horse or can work with someone (with a horse like this, it needs to be someone with a very calm demeanor) who does, I'd say yes buy him! It sounds like she is asking a little much for him. I would give her the numbers everyone else has given, and offer a lower price.
One thing I have heard about horses like this, and it was true for Teddy, is that they can internalize a lot of anxiety and then sometimes they might blow. Teddy apparently did that once. And he can NOT handle an anxious rider. So if you're taking him as a project to re-sell, you might have to be thoughtful about potential buyers. And to reiterate, whoever trains him needs to be calm, patient, and understanding. As an example, I rode him in a group lesson once with the yelly instructor, who makes him nervous. So he got worried and couldn't stand still when it was the other person's turn to do something. So she yelled at him and then thunked him. Well, guess what, that just made him more worrried and anxious and less able to stand still. I ended up leaving the lesson early because he was just getting more and more anxious. At some point, I'd like him to be able to deal with that sort of thing, but it will have to be a slow approach.
In short -- be aware, but take him! Save his life! You can do it! Just be ready to be very patient and move as slowly as necessary.