First of all, the few commenters were right about the electric. BUT, that's because it turns out that even though the knob and tube is only on 4 circuits, it's wired to almost every light fixture and outlet in the house. How is that even possible? Who knows. But we do need to make the house safe, so we'll probably move forward with the rewiring. It will encompass the basement, first, and second floors (minus the kitchen, since we'll be gutting that next spring if all goes according to plan).
So far we've gotten 3 quotes (waiting on 2 more) that range from $7,500 - $13,000. Yikes. Just a leeeetle over our $3,000 off-the-cuff estimate.
On the bright side, the heating and air conditioning should come well within our estimate. So far our prices have ranged from about $6,000-$8,500 for similar systems (from what I can tell). None of them will be able to heat/cool the 3rd floor efficiently, so we'll have to decide whether to live with the baseboard heat and window a/c up there, or to put in a ductless heating and air unit for the 3rd floor. I suppose it depends how much that'd run us! One HVAC installer quoted $3,300 for that, which seems excessive. If we can keep it closer to $1,500 I think we'd go for it.
I'm hoping that we'll have all of the quotes in by the end of this week and decisions made next week. Then it'll be moving on to refinishing the floors...