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.