I agree that there is lots of variation - I did say my numbers were pulled out of the air.
To be honest, I had not thought much about the cost issue - I am used to sane health systems where doctors get paid for their time and treatments are paid for by taxes (or a similar system). If you live in a country where patients or third-parties pay for the treatments and doctors get a cut of that fee, then I can appreciate they could be tempted to pick expensive and unnecessary treatments.
You know a condition for which millions of random folk on the internet know better than the average doctor? That sounds hard to believe.
Agreed. But it is unlikely that a random guy off the internet can give significantly better advice on where to look than anyone else can get with careful searching. Remember, "it worked for me" information, websites, or remedies are /not/ helpful - what you want is "this is a reliable source of information with a statistically significant chance of increasing the likelihood of patients with this malady or symptoms getting better treatment". "I know someone who had that problem, and they found help here" does not cut it.
It is also a condition where people are sometimes worse off because they try things they find themselves, rather than following the doctor's suggestions.
With many conditions - including many cancers - there's a fair amount of luck involved. That includes bad luck when the doctor picks the wrong treatment, and good luck when the alternative treatment happens to work (or, often, is completely irrelevant to the patient improving due to other factors). The fact that a particular alternative has happened to help in other cases does /not/ mean it is a sensible idea for any other case.
That is why scientific medical trials are so essential - despite the costs and efforts, despite knowing that some people involved are not getting the best treatment possible.
Now, if you know of newer medical trial evidence and your doctor is out of date, it's a different matter - as noted before, doctors are still fallible humans.