"Administrative costs have been estimated to represent 25% to 31% of total health care expenditures in the United States, a proportion twice that found in Canada and significantly greater than in all other Organization for Economic Co-operation and Development member nations for which such costs have been studied."
So before we even get into the proportion of admin costs from BIR, you have to cut your number in half. I don't think admin costs are going to end up the real story in US health care. It's overpaying practitioners and overprescribing procedures. There are more MRI machines in Massachusetts than in all of Canada.
Here's JAMA for the BIR, based directly on cost breakdowns in specific real systems:
https://jamanetwork.com/journals/jama/fullarticle/2673148