welcome to YT!
don't ever buy an animal from a pet store.(their dogs are from puppy mills) it doesn't matter what kind of animal really. it's never a good idea to buy an animal from the pet store.
i am happy for you that your parents agreed to let you have a small dog. but there are a few things for you to consider given your age.
i think someone already mentioned to you about moving out. i don't know what your future plans are. but if you are moving out of your parents house, going to college. it will be VERY difficult to have a dog. because you have to find an apartment that allows dogs, (usually apartments will charge you more to have a dog, where i live, the places that allow dogs, you have to pay $100 extra a month to have a dog, and also, you have to put a bigger deposit down) and between school and friends and partying, will you have enough time for your dog?
i don't know what you want to do with your new puppy, but it can be kind of expensive. just to give you an idea. vet visits.($50 each time just for an appt. to talk to the vet, plus $ whatever service you need) shots. medicine/vitamins/food/toys. (depends on what you buy) puppy school. ($200) spay/neuter surgery ($600) emergency surgeries (milu broke her teeth, the surgery was $350) (but someone here had to pay $3,500 when their yorkie broke its leg), pet insurance (depends on the insurance plan) initial investment (dog crate, dog pen, leash, harness...etc.)
anyways, that's not all of it, but just wanted to give you an idea of what possible costs there are associated with a dog. if your parents are going to help you pay for everything. then you should be ok. but i know that if i was 19, then i wouldn't be able to afford to have a dog.
i've heard someone here (a younger person) say that they've saved up all the emergency funds before they got their dog, which i thought was a good idea.
i don't want to discourage you, but i just want to let you know the points that maybe you have not considered yet. so you will be prepared when you make your decision.
as for the price of the dog. i think it depends on the breeder you find and it also depends on your location. there are more breeders in some areas of the country, then that will make it easier for you to find a puppy. but if you do find a good breeder, they will probably ask you those $$$ questions as well, they will want to know how to plan to pay and care for the puppy if it gets sick.
good luck to you! and feel free to ask any questions you have, there are a lot of knowledgeable members on this site!