You forgot to add the value of the materials it is made of. You have the price tag for a house of X sq.ft made of ordinary materials, but what could be the cost of building it out of complete ICE??
Ice is a lot cheaper than standard materials I think. I mean the novelty of it is cool and all but when it comes down to it ice is not only a crap building material (how do you stay warm and ALIVE without melting the palace) and generally ice is less sought after/more plentiful.