Some vets offer their own plans, which in theory should not be extortionate, because they know your cats health history, but who knows in practice!
You could of course go down the "threatening to look elsewhere" route, many friends have done this with car insurance and have found that the provider can suddenly offer a better deal.
I believe that when the subject of pet insurance came up on here before, some GN members said that rather than pay the ever increasing premiums, they put a monthly sum aside to cover vet bills.