Seattle-based real estate site Zillow is well known for its Zestimate, its computer-calculated valuation of homes using nearby sales and listings. Well, the firm has run the Zestimate for the White House, and calculated it's worth $294.9M--if you were to list it with your friendly neighborhood real estate agent. Zillow said it calculated the value of the White House, as if it were a home that could be bought and sold, using its proprietary Zestimate algorithm. The cost of a mortgage on the White House? $1,130,832 a month, on a standard, 30-year fixed rate mortgage at 20 percent down, and 3.275 percent interest.