Treatment/putting an animal down at the vet's can indeed be expensive, but fully-qualified vets have had a very long University course to complete, similar to the Med School courses. Also, most vets have additional work to do at farms, testing cattle etc for TB and treating outbreaks of various diseases.
They also have to deal with grief-stricken pet-owners after putting their pet to sleep. I have had experience of wonderful vets many many times, and have always been grateful for their expertise, knowledge and compassion. To complain about charges (as many people do) is rather mean in my view.