Yes, it must have been taxes.
Value you declare there is for tax purposes only, NOT for insured shipping. (if the package was lost/damaged you wouldn't have gotten 500 US$ simply because you declared it that value)
Amiga Center is in france; they have an import tax on goods; that comes pretty close to 87 euro's.
Shipping to europe always mark the package as gift (if possible) and declare it's value under 40 US$.
