I can't afford a $1000 vet bill, but I do.. It's a priority for me, so I will always have the money somehow to pay for whatever they need. And I'm by FAR not middle class.
If you make it a priority, it's not that big of a burden, IMO... Everybody I know who can't afford a treatment spends the money elsewhere. It's not that they don't have the money, they just choose to spend it on other things. If you don't have money to spend on an animal, don't get one. If you're going to watch it suffer because you don't think it's worth the money, don't get one.
It's not about rich or poor, it's about priorities.