It's easy to compare prices on cameras, vacations, and homes. But in the United States, patients fly blind when paying for health care. People typically don't find out how much any given medical procedure costs until well after they receive treatment, be it a blood draw or major surgery.

This lack of transparency has contributed to huge disparities in the cost of procedures. According to Castlight Health, a startup based in San Francisco, a colonoscopy costs anywhere from $563 to $3,967 within a single zip code. EKGs can range from $27 to $143, while the price for a set of three spinal x-rays varies from as little as $38 to as high as $162.

When someone else is picking up the tab, mystery pricing is not much of a problem. But these days, even the 59.5 million Americans who get health benefits through large self-insured employers are increasingly expected to pay a percentage of the costs for their medical care.