If the item (or the entire shipment) is under $20, there is no duty or sales tax.
If the item (or the dress and wig) cost more than $20 , there will be sales tax and a service fee from the shipper, but there may or may not be duty.
There is no duty if the item is manufactured in a NAFTA country (USA, Chile, Mexico or Canada). But if the item is made elsewhere (like China) there is duty even if the seller was in a NAFTA country.
That's the simple part.
These are costumes for a child? Fairly cheap?
You probably won't be charged anything if you buy from overseas and the seller ships by mail. (Long story why). But you might.
You probably won't be charged anything if you buy from the USA and the seller ships by mail.
You will certainly be charged duty (if any) sales tax and a $5 or so service fee if the listing has these words.
Customs services and international tracking provided
That means the seller is using the Global Shipping Program. If your items will be under $100 do not buy from a seller using this program (Another long story). Over $100 and you may save money on import costs.
