When buying anything from the USA you need to make sure that you are aware of the mode of postage/freight before you pay. Some are very fair and some are complete rip-offs. Many sites often advertise 'Free Shipping' but when it comes to paying you're charged some exorbitant fee for freight, the 'USA only' sign can be viewed somewhere obscure.
I've had it a couple of times that the Paypal payment went through, and after that I get a statement to pay additional freight. Even if the freight is reasonable, I always cancel those transactions as business needs to learn that the internet is for the whole world, not just USA.
At the same time, there are good US businesses who are fair and efficient so look around. If not sure look online for reviews.