Contractor Costs

My parents recently renovated our home (my old high school bedroom is now an office – thanks, Dad). When they happened to mention how much it cost, I couldn’t believe it. They have been pretty generous with me, but I’m paying for a lot of college myself, and I was stunned to find out that they’d take on such a pricey project in our house. On top of that, I’m worried they got ripped off by their contractor. I’ve been upset about this for a while now, and I’m not sure how or if I should broach the subject with them again. Any advice?