Well, if you are not sure, make it cheaper than you think it should be and use it for an adventure plot or hook (clear out the rats/ghosts/etc, some evil/good guy's stash). And you can always use it for future plot hooks that siut your needs.
You could for instance have the house be sentient and able to "materialise" ghosts to scare people that it does not like. Now have the house like the rest of the party but not the new owner so he is the only one that can see the 'ghost' or reverse the situation.