First, old 78 RPM records, besides being historical artifacts, are very fragile like fine pottery or china and should be treated as such. As with sending anything through the USPS, if you are concerned with the price of shipping supplies, the USPS gives you, for FREE, all the tape, boxes and labels you need if you ship using Priority mail. You need to select the appropriate sized box for the item that you are shipping. It should go without saying, but the Priority boxes are meant to be used as boxes and NOT mailed flat like an envelope. Some people just don't get the concept that boxes are meant to be assembled as boxes and NOT envelopes!
Because of their fragility, the key to shipping old shellack 78s is to protect them from heat(they do warp), stress(they don't bend) and impact(like china, sudden shock will shatter them). It doesn't matter if and how much you insure a package for, if it isn't packed properly, don't expect insurance to pay! When you shake a package and the contents move or rattle, the items probably will not arrive in one piece! Below are some suggestions for packing:
You can make a cardboard sandwich of multi-layers of flat pieces of corrugated cardboard in squares(not the flimsy Asian stuff) using three layers on each side of the 78. To get real fancy, you can cut a hole in the center of one piece that the 78 will fit through so that it is surrounded by cardboard, even the edges. The square pieces of cardboard should be at least two inches larger than the record and the record should be centered on the sheets so that a bump on the edge won't touch the record. Some people use flat thick sheets of styrofoam instead of cardboard, but good cardboard is readily available and you can usually get it for free from cardboard recyling bins at stores. When shipping multiple 78s, one full square of cardboard between each record is recommended. The sandwich should be taped around the circumference holding it all together. You can also tape across the sandwich, but be careful not to tape it so tightly that it starts to bend the sandwich, puting stress on the records inside. It is best to wrap the sandwich in bubblewrap and then put it in a cardboard box for shipping. The sandwich alone is usually sufficient for shipping, if you are feeling lucky. Nothing is foolproof, as we are at the mercy of the shipping company once it leaves our hands.
Here are some ways that ANY records should definitely NOT be shipped.
1.) In thin cardboard envelopes like USPS, FEDEX or office supply stores have for mailing letters and pictures. Believe me, an eBay seller actually sent me an Elvis 78 in a Priority letter envelope! Guess what happenned? I have never seen a record in so many pieces when I openned the envelope!
2.) In bubblepack or padded envelopes. These have absolutely NO protection against bending or crushing.
3.) In boxes stacked or piled loosely with NO kind of insulation, support or separation of the records from each other. I have received boxes of 45s and 78s packed this way with a few to all of the records arriving broken!
4.) Never tape the record or record in a sleeve to the inside of the package without first putting the item in a sealed plastic bag(like a sandwich bag) or fully wrapping it in paper. I received an Elvis EP that had been placed inside a standard plastic record storage sleeve and then the person taped it to the inside of the package, including the open end of the plastic sleeve. Needless to say, the tape loosened on the open end of the plastic sleeve and the paper record picture sleeve slid out, the tape stuck to it, and tore out a piece of the picture sleeve! The act of a real braintrust here!