Some of your estimates on this seem fine, but not this:

liability, both for the vehicle and for the medical treatment; that's about $12k per year.

Insurance on my SUV is close to $3,000 a year, but with the understanding I drive it about 12k miles, and I'm not allowed to speed or run red lights whereas they're guaranteed to be speeding, and driving it around all day and maybe all night. And the ambulance is worth 5x as much as my car is. So I'd be shocked if the combo of their auto insurance + insurance against being sued for rescuing someone wrong is that cheap.