The point was made a couple of times, but has been overlooked?
In an Emergency vet clinic you will have 3-4 staff on hand at all times. That is the Vets fees plus $600 per shift to pay out in wages, let alone the medical supply costs. There are all the other costs as well.
Against that you have a number of pets in house for treatment. Some vets are more reasonable than others, but the Emerg clinic is a business without ties, or loyalties, to clientele. It exists to provide a service for a profit. No different than a private hospital or clinic for people.