Shipping a package from the US to Europe [closed]

The cheapest option will definitely to have them transported via the sea. Now the question is more about the volume... One hundred books will probably represent 3-4 boxes depending on the size of the books. Probably more than 50 Kgs. If you send it via a regular carrier, it will cost you a lot of money. I have performed some simulations with GLS and Fedex and it will cost you above 500 €.

Sea transportation usually require a minimum volume. The carriers won't really bother transporting few boxes. Most of them are looking for at least a container or few pallets.

When I first moved from the UK to the US, back in 1991, we used a shipping agent whose basic unit was the tea chest. I called them, they turned up at my London digs and dropped off as many empty tea chests as I'd said I wanted. I packed them and rang, they turned up and collected the full and unused ones. I paid a flat rate per full chest, and they went away. Some ten weeks later the full chests were delivered to my Boston digs.

I post this mostly to let you know that there is a middle ground, people who are interested in shipping more than a parcel and less than a container, and I'm fairly sure google will dig some out for you (I found a couple in minutes, but they're UK-based).