Other posters have given you great advice. I just want to add that, sometimes, when you pay so little for a pup, you end up paying big time in the future. I think if a pup is this cheap, it is fair to assume that health tests weren't done as these are expensive. You could end up with a pup that has many health issues.
I would also be careful of ads that say so little. Imagine, if it were your puppy that you were selling, wouldn't you include more info? I know I would.
I believe all of this because of personal experience. My first puppy, Cash, was from a bad breeder and I am still paying for it. Not health-wise, he is very healthy. But he is also 10lbs and way over standard. His colour, although beautiful, isn't considered a proper colour for yorkies.
The main problem with him was his behaviour issues. He had no problem living in his own filth and he is very aggressive with strange people.
My new puppy, June, is from a hobby breeder who breeds about two litters a year, usually only one. I paid a lot more for June, but she is totally worth it. She is 3lbs at 5 months and is the most adorable, lovable puppy ever.
Everyone comments on how happy she is.
I just don't want you to make the same mistake that I did. Take your time and find a reputable breeder, otherwise you might end up with a dog that you aren't happy with. If you want a proper yorkie, go to the proper people.
Good luck with your search!
Ps. I love Cash and I wouldn't trade him for anything, but I know I would make a better choice if I could do it over again. The difference between him and June just highlights the difference between breeders for me.