Last time I saw a hard figure on it, which was admittedly a long time ago, was while I was working at an immediate care clinic. Uninsured folks were getting billed roughly 170% what insured folks were thanks to these negotiated rates.
As someone who has paid out-of-pocket for an MRI (it needed to get done ASAP for logistical reasons and there was a bookkeeping screwup with my insurance): the markup for out-of-coverage services can be way way more than 170%.
Virtually everyone is insured as a side effect of being an employee at a company that provides access to a group health insurance plan as a benefit. This has the side effect of coupling people's jobs to their health insurance, which drastically reduces labor mobility.
