You will honestly be surprised by how much cheaper vet rates are for farm animals in comparison to dogs and horses and cats. Vets for all they are castigated for their rates do try to keep the farm animal costs down, Im sure the pet animal rates partly subsidise this and I think thats a good thing as a healthy food supply free from disease and suffering is critical for the nation, and there arent the PDSAs for struggling livestock owners.
Do pick up the phone tho, you will save money if it saves the rest of the flock and if you can get the sheep to them it should be even cheaper.
If I ever have to call out the vet to a sheep I know thats the value of that animal gone, but that's how it works with livestock. The flip side is that if the animal recovers well (eg had one with twin lamb disease), they are fattened and sent off that year as I cant afford repeat offenders!