A friend is moving from San Francisco to Paris, and I told him about a very low-cost option to ship books in bulk, the US Postal Service Airmail M-Bag. I used this service ten years ago when shipping books back from Yale to Paris, some of them were slightly battered in transit but all in all a remarkable service. It is also available for domestic use.
You basically buy the right to send a whole postal mail bag at a wholesale price, which comes to slightly under a dollar per pound for France. Interestingly, the French post office does not offer M-Bags to French customers but will accept those sent by the USPS.