How much does it cost to sell a existing product on Amazon?

So I was wondering how much it would cost to apply to sell an existing product on Amazon. I already created a new listing on Amazon from scratch and it wasn’t easy and I haven’t gotten any sales yet so I’m tempted to sell an existing listing in addition to the product that I already have my dad told me not to take any chances but it seems like there could be an upside to selling a more established product if I can still turn a profit and get more sales.