The best way I have found is to loosen the strings on the bass. Find or make a cardboard box that is is 52x8x20 or slightly smaller. Put the bass and case in it. Fill the sides with cardboard, packing materials or wadded up newspaper.Write FRAGILE in big letters all over the box. If you keep to that size, you should be able to ship to anywhere in the lower 48 states for under $80 through the United States Postal Service - Parcel Select insured. Prices go up if you exceed a 108 inch length + girth. If they try to charge you more, argue with them, have them measure the package and prove to you that the package is less than or equal to 108 inches length plus girth - a lot of postal workers do not know all of the rates, particularly for large packages. If you have a way to print postage at home you can bypass the hassle of dealing with postal employees entirely. I have shipped more than 240 of my converted baritone guitars all over the US and Europe that way with good results. Prices to most countries that accept a 108 length + girth package are under $140 and that includes much of Europe and the UK.