Where costs will inevitably get complicated are:
1. emergency medicine, where the purchaser is in severe pain or possibly unconscious.
2. conditions without cures, or possibly even well-established treatments, and there is thus active experimentation and disagreement
Both of these are unpredictably expensive to an extraordinary degree, and the second category is sometimes rare enough that economies of scale don’t come into play for individual conditions.
I think government coverage of emergency medicine, aka ERs for severe injuries, is relatively uncontroversial due to its nature of treating unconscious patients.
However, that other category is very large in modern medicine. It includes all chronic conditions without cures, for which many options are available and improved techniques are constantly sought - and it includes complicated conditions where treatment has risks involved, which is basically a huge range of surgeries.
The problem in these areas is that the consumer does not have adequate understanding of the efficacy of what they’re buying, yet they’re driven to buy it strongly by pain and suffering. They are likely to want to do whatever a doctor or hospital tells them to do.
What is needed here is a consumer advocate with medical knowledge to keep prices consistent. In the US, this is provided by a mixture of regulation, medical malpractice lawsuits, and insurance companies.
Insurance companies are now failing in that role, but removing them entirely without any sort of replacement is going to leave the courts as the major vehicle to manage the costs - that isn’t a system renowned for efficiency.
It's a bad idea because of the state of the rest of healthcare _due to the state of health insurance_, but nothing prevents you from self-insuring.
Health care is yet another of those services where society as a whole does better if everyone's needs as a whole are considered and taken care of together. It is definitely frustrating for those who have more and wish to pay more to get better care, but heck, it's still a better deal in that case. There are all kinds of diseases that have been eradicated (or are on the way out) due to a broad social program to first discover and then distribute the cure. Paying for the very best leprosy care yourself pales in comparison to never catching it.