Cheapest way to send to Greece?

I am in the process of negotiating a swap with a fellow Greece member and I have a question for US members.

What is the max max amount of weight I can send that would still fall under the $30-some for shipping? And how much weight does the box and packaging and tape and all that fun stuff usually weighs when the box is sealed?

I once was 3 grams over the limit and they charged me more.

a 1st class package is $14.00 up to 8 ounces.
if its 8.1 ounces up to 2 pounds is $23.50
a padded mailer weighs less than one ounce.
a small cardboard box might be 3 or 4 ounces.

Thank you! The info really helped!