Through thousands of years of breeding the smallest with the smallest and the largest with the largest, there are now three distinct sizes of Poodles recognized by the AKC: Standard, (over 15 inches at the highest point of the shoulders), Miniature, and Toy (under 10 inches).
There is no such thing as a registered Teacup Poodle. The term is used as a marketing gimmick to indicate that the puppy will be extra small, commonly 2 1/2 to 4 pounds when full grown. However tiny Teacup Poodles often have serious health problems, which may be why they are so small in the first place.
In many ways they are like premature babies. In nature they would seldom survive puppyhood. They need constant human care and nurturing. If they survive, they often have lifespans of 3 to 5 years instead of the expected 12-15+ years of a toy or miniature Poodle.
These tiny puppies should cost less than a normal size healthy puppy because they require special care and generally have higher medical expenses, but often a breeder will charge more for them.
For most people a "Teacup" puppy is a bad idea. Besides health and dental problems, they are quite delicate. Jumping from a chair or being stepped on can cause serious injury. They should never go into a home with children or a lot of activity unless they are kept in a draft-free crate or cage.
In which case, as my email friend Rita says, “You might as well put a Poodle costume on a rat or hamster.”