On $14.89 I pay FVf of $1.48 plus paypal of 66 cents.
On $15.80 I pay FVF of $1.58 plus paypal about 79 cents.
That does not recover packaging materials or include any small handling fee.
It also does not include the twenty minutes to deliver the item to the post office as without lodgement proof I lose a very high percentage of parcels. My time is charged at fifty dollars per hour so to post one parcel costs about $17.00. If I am lucky enough to make multiple sales in one day then that cost reduces.
if you choose to offer free post that is fine, but when you post at cost and try to make a small profit from items you sell then you need to recover costs in a realistic manner.