Priority Mail.

USPS won't ship it because the box is too big: 39x28x8 in.

A frameset should be WAY smaller.

I had to call USPS last winter because my daughter crashed in CA, luckily the winter camp was right near the Felt head office, and she got a replacement bike. I had to send the cracked frameset back to Canada. I paid a little more than $120. for the parcel (bike without wheels) and go figure couldn't get a decent insurance amount on the bike (It was still mounted with Ultegra 8000, Rotor P2M crankset) with the options from USPS...

Louis :-)