My Yorkie is very healthy too, but she had an accident where she fell wrong and busted her knee last week. It cost me $3500 to have her leg fixed. I'm glad that you are being responsible and making sure that you will be financially capable of caring for your Yorkie before buying one. Just to ease your mind a little, the surgeon said her injury was NOT due to her small size or her breed. This injury happens to big dogs, small dogs, horses and my HUSBAND! Your best bet for finding a strong and healthy pup is to get one from a reputable breeder. Maybe you can even find one here on YT
Good Luck!