For the sheep I do a pooled sample, just take a wee bit of several fresh droppings. Also if the sheep are on fresh ground, their droppings look like the above described raisins/smarties or whatever, I wouldn't worry too much about worms.
same for goats really. I do worm counts for my goats individually, but only if their droppings get a bit loose and their coats loose their shine a bit. But then worm the lot, so they all are on the same regime. Mine then go out onto same pasture, not much choice at the moment.
My vet also charges about 14 pounds per sample, but its a next day result, and I can take the sample to the local lab, just down the road. Too easy to try and save a few pounds, as the post office is in the same village!
But check for fluke - talk to the vet. S/He will know if it is a local problem. I do have it.