No doubt you'll love herding with your dog, it's magic. I usually go to an association (they don't make a living out of it), so I pay 25 euros annual fee + 20 euros each time I go for the day or 10 euros for half day. This is very cheap.
In August, I'll try something different with a professional and that will be 50 euros for the day. Prices differ from place to place.
I don't have private sessions, they're all group sessions but one dog at a time. There are 8 dogs per day, or 4 per half day. Usually, we herd about 15/20 minutes four times in a day which is ample enough. After that, your dog will be very quiet on the next day