Good explanation by Zero Degrees.
A little background:
Unfortunately anything that is beyond a regular physical (which is covered fully by insurance) is now considered a separate visit. This is super confusing and one of the unforeseen consequences of the provision, which doesn't take into account that patients usually talk to doctors about specific problems at these visits. What is happening now is since the insurance companies have to pay for the whole cost of an annual visit, they are trying to minimize what they consider an "annual physical" and also how much they pay the doctor. The end result is the physician has to differentiate between routine checks vs. specific problems in a single visit, otherwise their total reimbursement will drop substantially. You could see an extreme scenario where someone comes in with chest pain and thinks that a cardiac evaluation is part of their physical, when clearly making sure they aren't having a heart attack requires more in-depth evaluation than a routine exam.
This is yet another example of the problem with fee-for-service billing that makes physicians into penny-pinchers and helps create loop-holes for insurance companies. Whether the doctor does a full exam on the specific issue to justify their extra charge is another issue, and can lead to some dishonest doctors bilking physicians and companies to pay for their expensive lifestyle. On my end, I see the solution to the latter problem as being a Mustachian. I don't have a good stop-gap for the former. i will also note that the majority of the charges people get, especially for a large group practice, go to people other than the physician: secretaries, medical assistants, nurses, administrators, middle managers, boards, CEOs, janitors, utility companies, suppliers, etc.
Another point. The way that billing for a visit works is this:
1) There are 5 codes for a visit that account for how complex a visit is, based on history-taking and physical exam. This does not include any diagnostic testing. The patient's insurance company may or may not have an agreement for how much they will pay for each code. Therefore, the office may be able to tell you what the range for the visit is (from basic to highly complex), but depending on the complexity of the visit after, until the evaluation is over, they cannot tell you the total cost of the history and physical exam portion. The reason is they will not know before-hand exactly what they have to discuss at the visit to reach a diagnosis.
So now you have a range of prices, where you will fall in that range for a new issue is unknown until after the visit for reasons explained above. If it's the same thing every time you come in, then you will have a rough idea over time and it'll be one of the 5 codes most times. Also, it's cheaper for a recurrent issue than a new issue.
2) If an issue comes up that requires anything other than talking and a physical exam by the physician, such as a blood test, X-ray, a procedure, or anything else, that is not included in the cost described in (1). Those are billed separately. The office can tell you roughly how much each thing will cost, but again it varies based on your insurance company. This makes the range of your costs even wider. You can refuse to do the recommended tests. This will make the diagnosis less sure, and let your physician know so they can document it, but you don't have to do anything you don't want.
The summary being, if you and the doctor do the same thing every time (check your blood glucose, check your whatever routine lab), then you will know how much it costs. If it is a new issue, it is hard to know ahead of time. They can give you a rough estimate for the visit and for the subsequent tests, but those are very rough estimates.
If there's interest I can let you know roughly what Medicare pays for various things.