What makes you think they didn't do it for cheap? Because the article says they did it for 90k - you certainly shouldn't believe everything you read.
I wouldn't have touched it with a 10 foot pole either. That said - they don't have 90k worth of material in that building. They are a contractor so in essence the labor was free (it's a business expense) so go ahead and classify it however you want to classify it. They are not getting material, carpet, paint, drywall, insulation, electrical from Menards (although I love the place myself) they are paying half what you and I would pay for a project. My dad has worked in construction his entire life (still does), I have a fairly good idea how these things go down - especially in this town. I'd be surprised if he has half of 90k in that place. So go ahead and cut your cute math in half, not sounding so bad now is it?
From a personal standpoint, I two am glad they did it. Also from a personal standpoint, I two would not have considered doing something like this. At the same time I don't have the resources available to me that they have. But don't think for a min. that this is just a couple rich people from Terre Haute who decided to put 90k into a house and then an article in the Tribune Star. Look, this guy didn't make his money being a complete idiot. I have a hard time believing he would invest in something he couldn't either A. do for next to nothing or B. think he could make money doing.
Just my thoughts.