Finding coverage for snakes may not be very easy, the closest thing to it would be coverage used by farmers for their livestock.
If you are talking about health type insurance like the ones available for dogs and cats, it will in the long run cost you far more than what you will ever need to spend on vet care.
IMO the best way to go about this is to be disciplined and to put money aside in case issues arise.
It's funny you ask, as one of the offered benefits at my new job is pet insurance and it does cover exotics. The monthly nut for 80 snakes is more than I've spent on vet bills in the last 3 years though.