We don't have a specific number for our pets, but we have an idea of the efforts we'd do for each specific pet. Hubby and I have a combined-pet household, and the cats and dog are all over 10 years old now, so we're at the point where we'll keep them happy and healthy as best we can, which includes maintenance meds and special diet foods - the total cost of which I don't even want to think about. Other than those and taking them in for checkups or routine items, I don't see us doing any life-prolonging procedures for them.
All three cats are special needs, so a long, healthy life may not be in the cards. Thankfully, we've gone to the same vet for their entire lives, and the vet agrees with our stance of quality over quantity, so they give honest opinion to us on what is best for the pets given their conditions.
In the budget, we currently put $450 per month into the Pets category, which covers anything pet-related, and let the remaining balance roll over each month. We have over $2000 in there to cover medical costs.
As for pet insurance, I looked into it ~10 years ago for another dog because she had horrible allergies, but she had already been diagnosed, so everything would have been excluded under pre-existing conditions. I ended up self-insuring and continue to do so now because it's easier than fighting with an insurance company.