To explain shipping on
ebay from the seller standpoint is slightly complicated. If a coin under $20 ships for a dollar in the
ebay special envelope, yes it has tracking but it is awful. Coins often arrive much later than even regular mail would, often taking over two weeks. Most every issue I've ever had with a buyer was while using these, and have multiple times had to refund a buyer who did not receive the coin in three weeks, only to have him contact me later and say it did finally arrive. So I'm out the money and the coin. These are issues with the mail, not the seller, but late coins are a great way to get a poor feedback, which also matters.
So for the past several years I have refused to use that method, just using ground advantage. This year I upped my flat coin shipping rate to $5, yet the least expensive ground advantage rate for a tracked package is $5.40 and often more depending on region.
ebay also takes it's percentage from shipping rate as well, so it costs me at least $6 to mail any coin at all, before considering the cost of the envelope and packing material. So remember that sellers offering a low dollar coin can quickly lose money, or get a bad feedback, for very little per coin profit.