Bigal, if you ship them in a flat rate priority box than shipping will be the same, but may take an extra day to Hawaii, for example.
If you have regular boxes and ship priority then it's by weight.
It's cheaper if you print out the labels using paypal and they also generate your tracking number.
I just box everything up print out the labels via paypal and drop my package off at the post office in the drop box inside... No waiting.
Hope this helps.
29g planted community tank, 2.5g mini bow work shrimp tank, 1.5g shrimp/growout tank