Buy a box from any of the storage/moving companies like UHaul etc, which will fit the AV/3 and the sub.
Then buy some roofing insulation Styrofoam from HD or lowes...this is a wonderful packing material - light weight, and yet offers very good protection. Pad the speakers with this material, and you should be fine.
I shipped a pair of super heavy weight speakers (~75 lbs each) using this method via DHL, and it reached the destination in perfect condition.