I got burned by this in California a decade ago. A dentist charged me $4,500 to fix a broken tooth (panic!) and fill in a cavity on a Sunday.
Had I known then what it might have cost I'd have simply flown back to Europe in the next flight ($600-800 at the time) and get the same thing done for under $100-200 with a full refund from my local social security.
Adding insult to injury I had a very expensive international health insurance policy owing to my traveling around the world back then. And they didn't cover dental with my plan. I knew they wouldn't. But it was still mind boggling to me in that I never expected a casual procedure that would have cost me €150 at most anywhere in Europe - most of which would have gotten refunded at that - to cost me a whopping $4,500 in the US.