While I agree that veterinary bills are very expensive, especially since I am struggling to make ends meet atm, there are many things that cause these bills to be so high. Keep in mind that a vets office has a lot of expenses. Salary for highly educated employees, continued training courses to keep their knowledge up to date as medicine is an ever-changing field, diagnostic equipment and maintenance of it, professional cleaning and disinfection of the clinic space, insurances, VAT, system for keeping medical records, being stocked in materials and meds so they are prepared for "anything" at all times...
In my country veterinarians, vet nurses and assistants earn a lot less money than their colleagues in human medicine. Still as pet owners the prices seem unreasonably high. Unfortunately medical care is expensive. I would never risk not having insurance, not on my house or my car, and definitely not on my beloved pet. It is annoying that it is necessary, but that is just the way it is.
My cocker managed to steal some chocolate the other day, that mistake cost me over £100. All my dog needed was two injections. But I am paying for the time the vet and nurse spends with my dog in addition to the medicine itself. And if they don't cover the expenses of the clinic by charging costumers, then there won't be a clinic there to help our pets.
The only way to control how much vet care will cost us is insurance. I think we would be better served trying to get better deals from insurance companies than from pressuring vets to lower prices. I feel your frustration, I am currently struggling financially and the vet bills are a huge problem for me. But having seen it from the other side too I know that the money I leave at the vets will need to cover much more than just the salary of the person treating my dog.
I'm usually very honest with my vet. If money is tight I tell them. My dog is my baby and I want the best care for her, I'll scrape together the funds I need somehow. But if the medical treatment is likely to fail I would rather do the more expensive surgery and get it over with. Or if the medical treatment has a high success rate then I would prefer that option. If you have a decent vet with a solid education, then part of that education was about choosing treatments that are financially suitable to the costumer as well as securing animal welfare. Of course welfare should come first, but if a costumer indicates that money is an issue a compromise should be made when choosing an intervention (as long as it is responsible in regards to welfare).
Sorry for the long-winded reply. But I find that knowing where the money goes makes me less frustrated with the prices. I usually ask for a detailed invoice too, let's me see what the medicine costs, the treatment and how much is VAT.