Tonight's episode: Widow and three daughters lose house to massive fire. Team with a hundred workers builds them new house in a week. They also build a bed and breakfast in the upstairs, something the mom and her late husband always wanted to have. Then the contractor donated $71k for the girls' college fund. If you didn't cry a little seeing this, you aren't human.
Yes... you can make good TV, get ratings, and still do something good in the world.
I would imagine that most of the materials are donated. The time from most of the construction workers are donated as well.
Sears donates a lot of resources. I would imagine that the show yields a lot of tax deductions for companies like ABC and Sears.
Not to mention the good will feelings that it has from people toward the companies making the show happen.
I find it amazing what that team can accomplish in a week. Hell, it took me 14 months to paint a room!