The majority of vet costs are beginning of life and end of life. Similar to people care too actually. But you can do things to mitigate the costs. I'm doing that right now in fact.
I posted above somewhere about Arwen going to the vet for grooming. Well, we also did the really complete bloodwork ($300) because not grooming is not normal, and it came back as nonspecific "something is wrong", with the something very possibly being cancer. And something is wrong. Arwen isn't eating well, her behavior is way off, she's dropping weight. I could take her into the vet, do a bunch more tests and try to treat this. It likely wouldn't work, whatever it is has been going for months and by the time they're starting to refuse food, you're pretty much done. And Arwen doesn't like the vet. She doesn't like taking meds. Her entire personality is one which prefers low intervention.
And that's what I'm doing. I do have a vet appointment scheduled, but honestly, that will likely turn into an euthanasia appointment. I'm doing what I can to encourage her to eat - I've got the meat baby food, I got a variety of kitty junk foods to try, etc. It's not enough to maintain her weight but she simply isn't willing to eat more. So I'm spending $$ on the pureed foods that she seems be eating best right now, rather than $$$$ on vet care that won't be successful and will make her miserable.
This isn't easy. It requires that you be emotionally strong enough to accept the inevitable. It requires the willingness to put the animal's needs above your own. I have practice - Arwen will be the 4th cat I've lost since 2019, but it doesn't really make it easier. Each one has declined differently, and she's the first that I knew with certainty more than a day or two before the last vet appointment (it's day 4 of certain knowledge for me right now). I am currently a highly functional mess. Because I know that the cat who is currently purring on my lap is dying. Its hard. I've had her for 14 years, she is the first cat I adopted as a kitten and raised myself. She has given me all her love, and I will repay that debt.
It's not a money decision. I have the money. It's a philosophy that I am responsible for the health and wellbeing of the animals I own, and that includes a good death. It just happens to save a lot of money sometimes.
Update. Arwen did indeed have her vet appointment, actually right after she had a pretty rough night. Dehydrated and clearly ill, plus something going on with her belly making her quite uncomfortable. Vet looked at cat, looked at records, and suggested an x-ray, which hadn't been done yet. I thought this reasonable and agreed. X-ray showed air in her stomach and nothing else indicative. So, we had a dehydrated, non-grooming, non-eating cat with air in her stomach, and bloodwork/xray showing symptoms only, no cause.
Vet suggested one round of intervention, after which if it didn't work we'd know for sure she's end of life. That intervention? Fluids and a shot of antibiotics. At minimum, these would make her feel better temporarily, and then depending on what's wrong it might enable a recovery. Vet thinks the odds are against a recovery but that it was worth trying.
So that's what we did. She got fluids and the antibiotics, and is clearly feeling better now, as we expected. The real question is how long will it last. We have no idea what's wrong, we just have a list of stuff we know that it isn't. If she's unable to maintain or improve her condition and declines again, then vet and I agreed the next visit will be the last. It was actually pretty funny, the guy was going into the whole quality of life is most important spiel.
So, cost wise: $600 a few weeks ago for grooming, anesthesia and the really complete bloodwork (though that wasn't intended to be end of life care so technically I shouldn't include it), and $300 on Monday for xray, fluids, and antibiotic shot. Not nothing, not horrifically expensive, but humane and fair.
This is part of having pets. Its not easy. But the benefits I get from having cats outweighs the cost to me.
As for outlook right now: Arwen's feeling better, but that means all the symptoms have been dialed back. They're still there. She's eating better, but still needs a bit of coaxing to get enough food. Still not grooming. Still clingy. We'll see what happens.