There was a lengthy thread on the identical question about 2 or 3 years ago….unless some of these seforim are rare or high value items, using any commercial shipper via cargo ship is the lowest cost option, especially if you are able to find a shipper looking for smaller items fill a container. If you are concerned about reliability and timely delivery than a shipper like DHL can provide “as available” air cargo shipment at a higher cost but with real time tracking and more certainty. Really depends on the value of these seforim to you and how difficult they would be to replace if lost or damaged.