Not sure about US, but as rates go from Canada, for letter mail (NOT Packages) up to 100gr it costs CAD $7 (~US $5) and up to 200gr CAD $12 (~US $9), so it is somewhat similar to EU. If Canada Post deems the package as “non standard” (i.e. dimensions/weight) and requires customs declaration form then it is considered a “small package” and starts at around CAD $13 going up from there based on size & weight.
I guess the “high shipping cost” is a relative term. If the swap is for coins valued at around 16 euros, 8 euros for shipping adds 50% to the cost of the exchange which I would consider “high”. If the swap value is of 80 euros then the shipping costs is a much more reasonable 10%. Wouldn't you agree?