If like fp have inflated transport costs then yes.
i think shipitto have built in post quote to give you some idea if you can guess dimensions
also, some places only ship with ups, but us post would be cheaper.
These guys give you several shipping options.
but if you ship via sea freight, you pay gst no matter what the value is
usps definately have a parcel quoting service online to check your seller is doing the right thing.