Update: just moved my family home (across continents, into a city), and it cost 278 gold for the character, and another 278 for the family.
There's probably multiple factors that affect the cost, though they are not transparent it would seem. When I did it years ago, it was a flat 300, all from my character. Clearly that formula has been changed at some point in the interim. That or my memory is faulty (never a possibility to be discounted).
As far as uses go, yeah there's the stirring up unrest part. There's also visiting the family home for gold; it's like asking your family for gold, but works somewhat differently if I recall (not sure if it still works, actually, as it factored into an endless family gold exploit from a few years back that was eventually fixed). You can also find out some things about the region it's in when you visit it. Overall it's nothing amazing, more of a flavor thing since on your family page it lists where your family is from when other players view it. My original home was in Darka, but I moved it to Astrum a long time ago since I spent very little time in Darka (which I did not enjoy) whereas my family was deeply involved in Astrum's history up until about six months ago or so.
