> A new, fully equipped ambulance is about $150k.

This is definitely not true. A base model unequipped ambulance may be in that ballpark. A fully equipped ambulance will vary wildly in cost based on clinical level but will be about $250-500k in the US.

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

Maybe for BLS or non-emergency ambulances in a low-utilisation role? For ALS/Critical Care or higher in a busy jurisdiction it's going to be significantly higher.