I was recently in the same boat as you. I actually went with Prestashop Store Manager as it includes ebay and Amazon integrations and they work fairly well, but it also includes a lot of killer features that are really useful for product management, categories, importing / exporting, PoS etc. It is $359, but I did find a discount code to knock a bit off so it cost about the same as the eBay module but includes amazon and loads of useful features too. You also get a 14 day free trial so I would definitely say try store manager out first to test your idea. Their support has also been really good as well.
I am not affiliated or anything just sharing my experience of being in the same boat, hope it helps.