swapping to free selling

If I can swap to fee selling on an ID I am presently paying near 13% on say a $200 item I will pay near $30 not allowing the fees on postage. If I sell on free it will be just over $12 buyer fee instead. So seems I could reduce the item by $18 and everyone will be ahead as buyers fees will be even less as well with lower price. Am I doing the sums right here?