I'm sorry but when you do an internet search for a Yorkie puppy (or most any breed) all you are going to get are puppy mills and brokers. A large percentage of the various classified ads are puppy mills, brokers and backyard breeders. Of course any of these and actually many of them will charge $400 to $3000 for a puppy with poor bloodlines.(all of them from the same stock) Meaning that they have a good chance of having genetic issues.
Save your money. Add to it every month. Within a few months you will have the money you need to buy a nice pet quality pup from a reputable breeder. You should expect to pay from $1000 to $1500 for a nice pet quality puppy. As others have said that is just the start of your investment. Puppies need a lot of supplies when you are first starting out and of course you have the vet bills to pay. You have to calculate all those expenses into you budget as well. If you are not in a position to face those expenses then maybe you are not quite ready to take on a puppy.
When you are ready go to the AKC website and do a search for a conformation or breed club in your state or a neighboring one. These clubs have breeder referral people who can direct you to reputable breeders. They will only direct you to approved breeders. The clubs have a reputation to uphold.
American Kennel Club - Club Search and Directory
I know it is difficult not to jump at a deal online that sounds too good to be true but truly they are not true. There are some very bad people out there that are counting on your desire to have a cuddly puppy or sweet little dog to love. They prey on people who just want to love a little dog.