They talked about that on TV in Twin Cities - they commented that in Minnesota if an insurance plan doesn't have Mayo in network, it is harder to sell the policy - so I suspect the Minnesota BCBS Medicare Advantage plan is giving higher payment to Mayo.
Medicare sets the price for a procedure, and the remaining 20% is up to you. A Medigap supplemental policy will pay that 20% based on price Medicare established. A Medicare Advantage plan does not want to pay that 20% and wants to negotiate it down lower to increase their profits. So insurance company establish their own network of doctors who agree TO TAKE LESS than the 20%, and you are required to go to a doctor in their network.
Also, Mayo is only place nearby you can get Proton Beam therapy (There are only some 40+ places in US, Photon radiation (like SBRT) is common, and many places offer it. Also, they want certain tumor characteristics to use Proton Beam. So, your network could not offer best treatment option.
The actual cost is the total of copays for every doctor you saw during the year and any tests before going to Mayo? And the amount of time for referrals and approvals. In two years, I have now had two surgeries, two angiograms, I lost count of how many visits and scans- so do my doctors - I never see a bill and I make an appointment with whatever specialist I think I should see.
I remember my first surgery two years ago and the person pushing my wheelchair at the hospital said that Mayo had stopped taking Medicare - I think he meant Medicare Advantage as I have Medicare Original. There were and still are problems in Florida and Arizona.