Different country, but pointing out some reported data on actual costs:
https://www.stjohn.org.nz/news--info/news-articles/st-john-a...
In New Zealand one of the major ambulance services reports costs of around $615 including taxes per callout.
However, the charge passed onto the customer is set at $98 for medical emergencies. This is waived for accidents (covered by the government).
A $4000 ambulance bill is offensive and I don't think justifiable in any way.