Holy cow! $600-$1000?? We live in an at least MCOL city (very expensive compared to state averages), and the bill for my 17-year-old cat’s annual visits averages $80-100. When I lived in the East Bay about 7 years ago, the charges were similar. (No doubt they’ve increase, but I doubt 6 to 10-fold.
She is FIV+ as a result of being attacked by a stray 5-6 years ago, and starting to become symptomatic. We’re not even doing diagnostic work ups, as FIV is incurable. Trying to treat would make her miserable and would be pointless. As long as she eats and drinks ok and can wobble out to the back deck, that tells me she’s reasonably content, and we’ll continue to take it one day at a time. We’ve had two trips to the pet emergency hospital for UTIs (just as my children did when they were young, she doesn’t get sick during office hours), which averaged about $250 each.
I have gotten nothing but sympathy and support in my preference for palliative care from the regular vets and emergency vets, possibly because I’m a blubbering mess when the discussion arises.
I’m actually curious as to what exactly is going on inside her, but having her frightened and in pain and miserable from any testing far outweighs satisfying my curiosity.

I completely understand treating younger, otherwise healthy pets that are reasonably expected to make full recoveries.
At any rate, we self-insure.
The continuous execution of a sound strategy gives you the benefit of the strategy. That's what it's all about. --Rick Ferri