Has to be. I don't know of any free shipping service.
I sell a lot on ebay. They're always pushing me to offer "free shipping." I sometimes do, but I build shipping into the item's price. The bad thing for the buyer is that they can't get a combined shipping discount when they purchase multiple items, so they may actually pay more.
Prime is essentially a tax that gets you faster shipping, generally better customer service and faster delivery methods.
It may or may not be the best deal which is why it is important to log in as a non-member and compare prices with third party vendors + the cost of expedited shipping.