I do not have insurance for my dog. He has only needed treatment 3 times in 7 years. The vet is happy to accept payment by instalments if the bill is too high to pay all in one hit. I think most vets are the same.The last time he needed a vet, due to a cut foot, the bill was £150, the vet was happy to take 3 payments of £50 a month. I was paying £29 a month on an insurance policy.
You may be lucky and have an RSPCA or Blue Cross vet near you, if so treatment is free for those on a low income.