I was looking over the prizes on the website, and I don't think there's an option to take cash instead of the house. What I did see is that the prize includes, in addition to the furnished house and car, $500,000. My best guess is that the money is to cover the taxes. I know in the past that people who have won weren't able to keep the prizes because they couldn't pay the income tax on the prize. I think the addition of the cash prize was to help fix that.
Oh, and DD10 has decided that it is the perfect house for her. We entered, but I'm trying to explain statistics and probability to her. However I don't think the tween brain was designed for logic and probability. She's rather plan how many sleepovers she could have in the bunk room.