Tea cup Chihuahuas?  

There is no such thing as a 'teacup' chihuahua. Teacups of any breed are nothing more than a badly bred runt of the breed, often backyard breeders put two runts together to produce an even smaller runt with even more health problems. These teacups are notorious for having lots of health problems.

The real chihuahua breed is small enough anyway so I suggest you look into that instead. There are probably lots of them at your shelter, but if you do want to buy from a breeder I suggest you spend a lot of time questioning breeders and only buy from one who health-tests for genetic diseases (this is not the same as a simple vet check, you will need to see the results of these tests done - any responsible breeder will be happy to show these to you). If you happen to find any breeder that will not allow you to visit and see how and where the puppies are raised and/or have numerous breeds that he is breeding, then run, not walk, run away. Be prepared to be put on a waiting list to get a puppy from a responsible breeder. It may take some time and it may cost a bit more money but in return you know you will get a puppy that genetically has a much higher chance of being healthy and having a good temperament. Also you won't have supported any backyard breeders/puppy farms helping them to run their business.