Jaime Rosenthal, a senior at Washington University in St. Louis, called more than 100 hospitals in every state last summer, seeking prices for a hip replacement for a 62-year-old grandmother who was uninsured but had the means to pay herself.

The quotes she received might surprise even hardened health care economists: Only about half of the hospitals, including top-ranked orthopedic centers and community hospitals, could provide any sort of price estimate, despite repeated calls.

Those that could gave quotes that varied by a factor of more than 10, from $11,100 to $125,798.

Rosenthal's grandmother was fictitious, created for a summer research project on health care costs. But the findings, which form the basis of a paper released Monday by JAMA Internal Medicine, are likely to fan the debate on the unsustainable growth of U.S. health care costs and an opaque medical system in which prices are often hidden from consumers.

"Transparency is all the rage these days in government and business, but there has been little push for pricing transparency in health care, and there's virtually no information," said Dr. Peter Cram, an associate professor of internal medicine at the University of Iowa, who wrote the paper with Rosenthal.

"I can get the price for a car, for a can of oil, for a gallon of milk. But health care? That's not so easy."

Although many experts have said that Americans must become more discerning consumers to help rein in health care costs, the study illustrates how hard that can be.

"We've been trying to help patients get good value, but it is really hard to get price commitments from hospitals - we see this all the time," said Jeff Rice, the chief executive of Healthcare Blue Book, a company that collects data on medical procedures. "And even if they say $20,000, it often turns out $40,000 or $60,000."

Researchers emphasized that studies have found little consistent correlation between higher prices and better quality in U.S. health care. Cram said there was no data that "Mercedes" hip implants were better than cheaper options, for example.

Jamie Court, the president of Consumer Watchdog in Santa Monica, said: "If one hospital can put in a hip for $12,000, then every hospital should be able to do it." With such immense variation in prices, he said, "There is no real price. It's about profit."