With the bar taken off and packed in a box closest to the size of the saws, USPS Parcel Post shouldn't run you more the 30.00 It only take a few minutes to calculate shipping from their online shipping calculator.
If you are worrying about purging the tanks of fumes, I was taught to let it dry out then hold the tank under the exhaust pipe of a running vehicle and let the carbon monoxide do the work for you. It sounds like a pain but i don't think you are going to bring an air compressor, nitrogen bottles, or have a workshop where you could work on the chainsaws.