I want to buy teacup yorkie (miniature yorkshire terrier) how do i go about that & what is the cheapest way?

adopt
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well, the cheapest way is to find a responsible breeder of normal Yorkshire terriers, since a "teacup" will cost you more in vet bills over the years.

Or find one in a local china shop.
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I'm going to copy and paste this from the last person who asked this question a few hours ago.

Okay, here are all the things wrong with your question.

1. There is no such thing as a "teacup" dog. The only people who use that term are puppy mills and backyard breeders. All it really means is "poorly bred undersized runt".

2. The correct size for a Yorkie is 5-7lbs. Anything smaller than that is going to come with a huge host of health problems resulting from being a poorly bred runt. The vet bills you will rack up trying to keep those "tiny" dogs alive will easily add up to more than $2,800 just in the first few months.

3. Any purebred Yorkie pup is going to cost a heck of a lot more than $400. If you don't want to pay that much, don't limit your criteria to an expensive purebred puppy.

4. Breeders DO have the best dogs- however, they also breed to meet the breed standards, which means they breed the CORRECTLY sized Yorkies of 5-7lbs full grown. The only sources of ill-bred runts are puppy mills, backyard breeders, petstores, etc.

So you pretty much have 2 options… stop trying to be Paris Hilton, and accept that a healthy Yorkie is NOT going to weigh 2lbs, and invest in a quality dog from a reputable breeder, which will cost more in purchase price but less in long-term vet bills;

OR

Buy a cheap puppy mill runt that MIGHT live past 1 year (but highly doubtful) and will cost thousands of dollars in emergency vet care trying to keep it alive.

Or I guess option 3, accept the fact that you don't want to pay for a purebred puppy, and adopt a homeless dog from a shelter… saving a life is much cheaper and more rewarding than buying a purebred puppy.

http://www.barkrescue.net/teacup.htm
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Purebreed yorkies are not cheap- you can look at local resuce groups who will have the older ones, but most breeders spend a lot of time and money and do not sell them for 300.00 and the ones that come from puppy mills are still 500+, go adopt.
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Well, first off, there is no such thing as a teacup yorkie. And there are no miniature yorkies either. The standard for yorkies is 4~7 pounds. If you get one smaller than that, it is a runt or has been bred for that size which is also a huge problem for another answer.
I breed yorkies and mine are anywhere from 3.5 to 5.5 pounds. There is no "miniature" to that.
If you are concidering a yorkie, it will cost ALOT more than $200-$300. I breed Biewers and traditional yorkies and just a trad. yorkie starts at about $1000. That is because mine are breed standards. There are some out there that dont look like yorkies or are larger than 7~10 pounds that may cost that low. You DEFINATELY are not going to get a yorkie with papers or that looks like that cute little picture in your head.
I would ALWAYS suggest getting one from a breeder as well. If you purchase from a pet store, you are more than likely buying a puppy from a puppy mill and along comes the problems and health issues. Also, as with all small breeds, the vet bills alone are FAR more than 200-300 every year. Getting a Yorkie at $1000 is the cheap part. If you are financially not able to spend more than that, it may not be the breed for you.
I know I just popped your bubble but please remember, you get what you pay for. If you find one for that low….there is something wrong! Either health problems or LS (liver shunt) lines or its going to be HUGE when full grown. (double the 12 week weight to get a rough estimate)
I hope that helps. If you need any other help, please let me know.
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Biewer and traditional Yorkshire Terrier Breeder with over 7 years experience