It's worth remembering that veterinary care has come on no end.
In the 80s, my childhood dog had a slipped disc. It was diagnosed on the basis of symptoms - no scans available. The only treatment was painkillers, rest and, when that didn't work, euthanasia.
Fifteen years ago my dog had similar symptoms. She had an MRI (which found it was something else), steriods, and physio. We had to travel to London for the MRI, as it was unusual for a pet dog to have back then.
This autumn my current dog also had neck pain. My own vets has a CT scanner. She's had multiple CTs and MRIs, including with her moving, and might have had neurosurgery. Fortunately she didn't need it, but it was on the table as a possible option.
Clearly those options carry very different costs.
The reason vets bills can rack up in a way they never used to is because vets can do so so much more than they ever could. If you're not insured, then you need to be able to handle an unexpected bill in the tens of thousands. Because, if you can't, you may have to find yourself saying 'no' to a lifesaving option because of cost.