I don't understand. You say this is a healthy and robust puppy and then say he is going to top out at 3 pounds? Honestly, breeding small pups is asking for high veterinary bills imo.
As for high vet bills, anyone who is interested in a yorkie needs to definitely consider what they would do if the pup fractured a leg and needed surgery ... or ended up having a liver shunt (which can happen) and needed surgery. Other things that can crop up are pancreatitis...that can land a pup in the hospital for a few days...eye problems. Oh, the list goes on and on. I strongly suggest that you think about setting aside a fund or getting a credit card just in case. It is heartbreaking for a pup to have to be rehomed because the owner cannot afford the veterinary care. And, trust me, it is a common occurrence in this breed.
Another thing: they need dentals often every year. Sometimes you can get lucky and not need them (doubtful you will skip any with a 3 pound yorkie); but I just had to do every one of my pups this year. I had four wellness exams this past week and three dentals and the bill was $1391. So....right around 300 - 400 for each pup's yearly exam and testing and also dental. If you don't do them, you are bound to have problems down the road with your pup's health...kidney failure...cardiac problems. And, those things are costly and also shorten your pup's life. Very sad when I see this happen to pups.
Hope this helps a bit.