Welcome to YT Amanda! A word of advice: Take the time to look over the rules at the top of this section. Being a new member, I'm sure you overlooked it, but it has lots of advice and suggestions to aid you in your search:
From the section:
"We do not allow threads begging for free puppies or looking for puppies at extreme reduced costs. Yorkies are generally from $500 on up, with most being in the $1000 to $1500 range. Please do not post looking for Yorkies below $500. If your budget for a Yorkie does not allow for $500 or more, you may want to look into Yorkie rescues or adoptions of older Yorkies, as they may be better suited to your price range. Feel free to PM sellers with an offer, but the public forum is not a place to beg or whine for a Yorkie, nor post looking for a Yorkie under $500."
As mentioned, looking into a rescue may be a great option to fit your lower budget. You will be hard pressed to find a pup for only $400 due to the costs incurred by breeders when raising a litter alone.
Also, YT does not allow advertisement of "Teacup" Yorkies, as already mentioned, there is no such thing.
You may want to contact some breeders in your area and see if they will consider you should they have a smaller pup in a litter. Or, they may have breeding stock they are looking to retire that they would be willing to place for a lower cost.
Good luck with your search. Hopefully you will find the perfect fit soon.