Your medical bills have revealed that you're paying thousands of dollars in out-of-pocket costs for surgery and while plenty of you blamed Medicare and your health provider, that may be misguided.

As part of our investigation into out-of-pocket costs, Four Corners asked you to send in your medical bills. More than 700 people responded.

Some of you had paid tens of thousands in out-of-pocket costs, despite having private health cover.

One issue we found was bill creep, where a patient needs multiple procedures, tests and consultations for one ailment.

The bills pile up and many of them aren't covered by the private health insurer because they were incurred outside hospital, where by law, health funds are not allowed to operate.

Madonna Buiter's out-of-pocket costs for breast cancer treatment were almost $16,000 — a result of nearly 40 separate procedures and tests.

The mother of two said she and her husband were forced to spend what they'd saved for a house deposit to cover her gap costs.

"They say, 'Oh well, you should shop around and find a cheaper surgeon'," she told Four Corners.

"Well, that sounds great in theory, but on this side of my journey I can say now, when you're given that diagnosis, you have breast cancer, you need surgery. I don't know that that's realistic or reasonable at that time."

Ms Buiter said it was difficult to get a clear picture of the total costs she faced and her private health insurer was of little help.

"Running around from surgeon to surgeon … until I was booked for surgery they couldn't tell me even which anaesthetist I was seeing, so I couldn't even find out the charges there," she said.

Sorry, this video has expired Madonna Buiter is almost $16,000 out of pocket after surgery for cancer

The hidden fees

Alarmingly, several bills Four Corners saw showed that patients had been charged a booking or administration fee, which medical bodies say are not legal.

Many surgeons receive higher rebates from health funds if they've signed a contract agreeing not to charge a gap fee. So-called booking fees are a way of cheating that arrangement.

The highest booking fee Four Corners saw was more than $6,000.

"Booking fees or other fees beyond the surgical fee are in fact illegal and should not exist and that is unethical to be charging," Royal Australasian College of Surgeons president John Batten told Four Corners.

Four Corners has been told that patients should report it if they are charged a booking fee.

"If a patient sees a fee like that appearing on a statement, they need to ask their doctor what it was for and what the clinical or medical relevance of that is, and if they don't get a satisfactory answer, they should not pay that fee and they should discuss it with their health fund," Private Healthcare Australia chief executive officer Rachel David said.

Who's to blame?

Almost all of the people we spoke to didn't want to blame their surgeons for out-of-pocket costs, however health policy experts say that's exactly who we should be looking at.

Terry Barnes is a policy consultant who's been an adviser to two health ministers, including Tony Abbott. He says health insurers are an easy target.

"They've got partly a PR problem in terms of they're always seen as the bad guys, and they're convenient bad guys, because the product that they sell is highly unpopular. It's about as popular as a fart in a lift," he said.

"Medical providers are always seen as above reproach. They're saints in white coats."

Grattan Institute director of health Stephen Duckett says some surgeons are submitting "outrageous" bills.

"The doctors are able to charge whatever they like. It's almost impossible for insurance companies to set a premium that covers whatever some doctor charges and those fees may be an order of magnitude above what the schedule fee is," he said.

One of the problems is that in the 1940s, a constitutional amendment was made that forbids conscripting doctors to charge regulated fees.

So what can you do?

Discuss with your GP what he or she knows about the charging practices of the specialists they refer to.

There is no relationship between the size of a doctor's fee and how good they are, so ask to be referred to a surgeon who participates in a no gap or known gap scheme.

If the specialist wants you to have a test that isn't reimbursed by Medicare, then ask what difference that test will make to your care.

When in front of the specialist and after the course of care has been discussed, insist on talking about costs.

Be unembarrassed about querying any items you don't understand and tell them if you think you can't afford the fees suggested.

Most surgeons will tailor their fees if they know patients will have trouble paying.

Surgeons are running a business and fees are the way they make their money, so a discussion about how much they're charging is just a business transaction.

Refuse to pay a booking, administration or nursing fee and refer any such bill to your health fund, who will take it up with the surgeon directly.

And seek second opinions. They are your right.

Watch Dr Norman Swan's investigation, Mind the Gap, tonight on Four Corners.