Let's say you pay $20 a month for insurance - that's $240 a year. If you think that your vet bills for a year would exceed $240, then it's a good bet. It's not worth it to cover for standard maintenance for a healthy cat, but it would be very handy for major procedures such as surgery and multiple x-rays.
Most people in the USA pay all vet bills out of pocket. You might ask some local vets which pet insurance companies they work with.
After my latest round spending $350 at the vet trying to figure out why my oldest cat was vomiting 4-5 times a day, I finally got pet insurance for my younger one (the older has a pre-existing diagnosis now, of IBS, and it would be too expensive to get it for him). It's worth it. Mine covers vaccinations and routine exams, as well as the more expensive things like drugs, x-rays, and treatment for serious diseases.
