Which buyer are you referring to? Consumers paying cash can negotiate as much as they want, and often secure large discounts. Commercial health plans also negotiate hard with their network providers, although some of them play unethical tricks with PBMs to artificially inflate prescription drug prices. Medicare and Medicaid don't really negotiate with providers, they just set rates by arbitrary fiat and providers can take it or leave it. Medicare does have some statutory limitations on how they can negotiate drug prices, though.
Which doctors? Some specialists do quite well but many primary care physicians earn less than software developers, especially once you account for education expenses and ongoing mandatory professional expenses. What is the correct amount for them to earn anyway?
Example: https://worldpopulationreview.com/country-rankings/cost-of-i...
And why, in free market land, is a buyer of services and medication, not allowed to negotiate prices?