Welcome to YT. Sounds like you got bit by the IWannaYorkie bug. The Petland prices are outrageous for a non-AKC Yorkie. You really don't know what you are getting for your hard earned $$. I would run from the pup in the classified for a couple of reasons 1) you don't know the background of the pup and 2) the breeder is letting the pup go much too early.
Rescues are a great option if it would work for you. There are many pure bred Yorkies that are in great need of loving homes. If you want a "registered" Yorkie, then AKC is the way to go. Checking with the YTCA (Yorkshire Terrier Club of America) is a fantastic starting point.
It's best to stay focused on finding that perfect healthy pup that will fit with your family. It is so hard not to fall in love with each one you see, but be patient - your new baby is out there just waiting on you to find him/her.