I think there is credible research that US drug costs are primarily the result of a fragmented market and lack of collective bargaining. So a single buyer regime will by itself lower the prices since manufacturers will be forced to compete among themselves based on price and an objective metric of the therapeutic benefit - as opposed to marketing and the best sales network and "conference" benefits the prescribing physicians.

For example, if the generic option reduces the burden of disease by 10 DALYs and costs essentially ~0$ it will be fully covered, any other patented option with a 15 DALY average benefit will be covered up to a financial ceiling given by the total funding available and the extra 5DALY benefit it brings. A patented option that does not fit that ceiling will require patients to pay from their pocket, therefore cratering sales, therefore strongly incentivizing the pharmaceutical company to lower the price to fit the ceiling.

This is how other advanced countries lower spending on drugs without infringing on intellectual property - by forcing all manufacturers of all drugs for all diseases to compete on price, or risk selling basically nothing in that country until their patents expire. Since the marginal production cost of drugs is close to zero, it' always better to have some sales at some lower prices instead of no sales at a very profitable price.