It used to be possible to ship via small packages via the Post Office for very low cost. In the past 8 years that has changed so that only flat items below 1/4 inch in thickness can ship in a First Class envelope.

The Post Office needs a major investment in new sorting machinery to be able to automatically process small boxes and bagged items with irregular shapes.

The best deal for small packages of items is Ground Advantage. As of July 2, shipping a small 8 ounce box across the continental USA costs a minimum of $6.74. Sending a single  item that sells for less the shipping cost is unpopular.

Combining the shipping cost in the item price so that it is "free" increases the prices for everyone so the local shortest distance buyer pays more than they should. The other option is to sell items in quantity so that the shipping cost is small compared to the total order amount.

We are going to go the route of encouraging full boxes of multiple items and allowing mixing so that we can offer the most value for the least shipping cost.  As particular items emerge with high popularity we will begin using Amazon Prime in addition to Ebay for order processing.