Find a friend who's got a sail boat. Might be cheaper that way. Just take a little longer.
Shipping regulations for Lithium cells is very bad.
Ask your carriers if maybe you could package each set separately and then put those into a larger package. It might be stretching it, but they may take it that way. Also, perhaps ask them if you send them in cell rated packaging if you could send a batch. There are a few here in the Marketplace who sell 100's of cells and are able to do so legally. It might be because they are packaged a particular way.
Then again it might be because they bought a license to do so, I don't know.
Where are you sending from? Perhaps you could contact a local authorized shipper and see how much they'd charge to piggieback off their license (just a thought)