Can anyone tell me at what stage of pregnancy do you do an ultrasound?
And any idea on how much is costs?

My vet does them 21 days after the last breeding and it's about $50

I have them done at 28 days from ovulation; depending on the vet and the type of equipment they have prices can vary. I pay $100 but at this point, he is able to do dopplers on the puppies and be sure everyone has a heartbeat, he can see the sacs to see if they look healthy and gives me an estimated puppy count.

day 35 from first insemination is what's recommended by our vet- cost is $60 CND