There have been a bunch of home buying questions, but I don't think this one has been asked already (if it has please just point me!!)

We looked at a condo we liked this weekend, but there were several, somewhat substantial, improvements we'd want to make. Most were somewhat easy to estimate-- redoing a bathroom, redoing floors, stuff like that. I feel comfortable with a rough estimate we could find online.

But, some of the improvements are more intense-- like there is a low hanging duct going through one bedroom that we would want to reroute so it went through the ceiling. We don't really know where to start to figure out how much something like that would cost and we don't know any contractors personally who could help us out. I know most contractors don't want to come out and give you an estimate on a place you don't own, but we don't want to get locked into an offer without knowing what that kind of fix would entail. Any ideas on how you get around that kind of thing?