I order a similar amount myself and it's rare when I can find things on Amazon at considerably lower costs than eBay including shipping. eBay gives free or reduced shipping costs, depending on the seller, whereas Amazon charges higher shipping prices especially when you order under a certain amount or order items not covered under their free shipping which seems to happen way too often for my liking. Plus, their 2 day Prime guarantee really isn't in certain circumstances. I know 3 days was more the norm during my 30 day Prime trial membership. That's when I learned their guarantee comes with stipulations.
I might join Prime if eBay starts to fail me or when shipping price increases make it worthwhile. But as of now, been there, done that, had the free membership.