There is NO SAFE X-ray machine. It's ionizing radiation. None of its safe. Older X-ray machines use more radiation than newer ones. Even one that is only 7 years old or so. Unless a vet is adjusting the machine for every animal that goes in it, which I doubt happens, a cat is getting the same level as a lab. Which is unnecessary.
Comparing vets to pediatricians is crazy. For one, pediatricians can't refuse treatment due to nonpayment. They also cannot euthanize their patients. I could go on and on.

You do know how x-ray machines work, right? Like, how to get an image? For different tissue densities, you need to adjust the kv and the ma and the time otherwise you will get a ****ty picture. So sure you could blast a cat with the same amount of radiation as a labrador... but you sure wouldn't get an image that was diagnostic. WTH?!
So yes, we DO measure the tissue depth and change the kv and MaS for EVERY IMAGE we take. We even change the kv and MaS in between a DV and a lateral on the SAME PATIENT. I don't know what kind of dark ages you think we're operating in but many, many vet clinics these days are equiped with digital or computerised xray, don't know where you get this idea that we're all operating with 20yo machinery comes from.
Also, the average veterinarian wage is roughly 60,000-80,000pa. If we wanted to make money, TRUST ME, we would NOT have gone into this field! We go into veterinary medicine because we are passionate about animals, animal health and welfare, and the human animal bond. However that does not mean we should not get paid for what we do, and since most US veterinary students have student loans in the range of $100,000-300,000, that salary is mediocre at best. We constantly struggle, day in, day out, with the financial side of things - people who get pets and are not prepared to pay for the costs associated. That is not OUR fault. That fault is strictly the owner of the pet. In reality, we exhibit great value for money.
I'll run a scenario by you:
Dog comes in with a bleeding spleenic mass: total costs amount to ~$5000. Common scenario, especially in emergency practice (typically the most expensive area of vet med)
What are you getting for that:
Consultation and surgery performed by a vet with 8+ years of university based training, and atleast 5+ years in emergency medicine resulting in "fellowship" qualifications.
Ultrasound, x-rays (to check for mets), CBC, Biochem, electrolytes, blood typing.
Stabilisation including aggressive crystalloid therapy, colloids and blood transfusions if required.
Anaesthesia performed using the safest drugs avaliable (induction with propofol/alfaxalone and maintanence with isoflurane/sevoflurane inhalation, with a CRI of fentanyl). Monitored by a highly qualified nurse or vet, using ECG, constant BP, capnography, temperature etc. Constant warming provided via baer hugger.
Surgery going for around 1 hour in most cases. Surgery itself is the same - completely sterile environment, using the same instruments, suction, autoclaving techniques etc. Just the same as a human hospital.
Constant post-op monitoring and around the clock ICU care for 2-3 days, depending on the individual. Animals are far more resiliant to surgery than humans are, so they tend to go home sooner.
Go on... how much would that cost in a human hospital? $5000 may seem like a lot - but in reality its a BARGIN!