The cost billed to you or your insurer is likely to be between $400
and $1,500 or more. Medicare Part B covers 80 percent of the approved
amount. That leaves you responsible for the remaining 20 percent.
Ambulances are generally not allowed to charge you more than that 20
percent. Though, you will also be responsible for any remainder of
your Part B deductible.
https://insurify.com/health-insurance/knowledge/does-medicare-pay-for-ambulance-services/
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this info might be buried very deep on the medicaid website and on
other website - everyone says you pay 20% - but they dont tell you 20%
of WHAT - its friggin bizarre