I wouldn't cost up call-outs on a per animal basis, its whether your enterprise can justify the number of call-outs as a whole.
Absolutely.
The whole affording thing.... loads of people tell me I should make my hobby into an 'enterprise' which is kinda a nice idea HOWEVER... then I just feel i would be worrying and number crunching. By keeping it as my hobby, when I have an expense, I simply say to myself and others "OH well, I don't smoke or drink - this is my lifeline and my hobby so its worth any expense!" I do feel I would not be anywhere near at ease if I made it into a business.
Slightly (!??!) of tangent here, but the comments above were very though provoking for me!
And that's how it's done, Mallows. Our enterprise is on sufficient a scale that we absorb vet fees as a necessary cost. We do take animals
to the vet rather than calling them out if appropriate, but we do not consider the individual value of an animal when deciding whether or not it needs the vet. We may of course decide to cull an animal rather than embark on a course of treatment, but generally this is more with the animal's future welfare in mind rather than the specific £numbers.
One of the hardest decisions I've had to make was whether to get some bionic surgery for a collie with a broken bone inside his elbow. After a sleepless night weighing up the alternatives, I called the vet to say I did not think it was in the dog's or my best interests to go ahead with such an operation. Since the only alternatives I'd been given were destruction or a life of pain, I took him to the vet's to say goodbye to him. By the time I got there, they'd had a conference and decided to offer a much more pragmatic, simple op, with a much shorter recovery time and, importantly, a recognition that a working collie
needs to work and will, out of choice, ignore quite a bit of pain in order to do so. And yes, the simpler op was significantly cheaper too.
Every single day, I hug that collie dog with his dodgy elbow, and he and I both give thanks for that sensible vet and his second opinion.

Sorry, I've topic-hijacked. Anyway, the point was, as Steve says, farmers make whole-flock or whole-herd husbandry decisions on a veterinary basis; they do not withhold individual treatments on a financial basis.