I would hate to argue with your statement of $5 dollars (which would be 1/5th the price of an average 3* hotel room) for an ultra sound but a simple google search would be all you need to really say that figure is not correct. Most prices for testing in Thailand have not increased since 2009 so an ultra sound runs between 1000 - 3500 baht (if paid in cash) or $33 - $113 american. That price is without any other labs or test and doesn't include the actual doctors visit. Still a lot cheaper than in the U.S but you also have to remember that $33 american dollars will go a lot further in Thailand no matter what you are purchasing.
Also while the insurance industry might play a role in why health care is so expensive here and cheap overseas but in Thailand for example the Doctors make roughly 40% of U.S. doctors, Nurses make 20% and so on with all the other staff it takes to make up a hospital.