I see you are confused about how the bidding process in a single payer healthcare system works. Yes, the government pays. That is the single payer part. That doesn't mean the government provides the healthcare. If i need a medicine then my doctor (who owns his own practice and is paid through copay, fixed government sum and extra pay for certain procedures) prescribes it, then its bought by the pharmacy from a foreign company and billed to the government.

The government negotiates the price for every step of the process. They dictate the copay, the fixed sum per patient to the doctor, prices of all procedures, what medicines and treatments are covered, who gets to cover them, and at what price.

To determine what is covered, who gets to cover what and at what price the healthcare providers negotiates with the government. This ensures there is effective competition in the market and prices are managed effectively.