If you beat the game though you can get into House Hlaalu for free even if your in a different house. Talk to the duke in ebonheart and he'll make you grandmaster of hlaalu. Im not sure if you can have the haluu mansion though.

Oh and the telvani mansion is the best although its in the middle of nowhere.

 In my EVIL file I actually killed off everyone in the entire redoran guild house. I then cleared my name, so I have every house in that giant crab like structure.

In my regular file I am the grandmaster of the Telvanni so I own Uviriths grave manor