I've sold a fair amount on amazon, but I haven't done FBA (Fulfilled By Amazon). I hated it doing it though, because I was charging a higher price, but making less money. I figured I could offer customers a better price when selling direct, so I stopped doing Amazon.
The thing about amazon prices is that they tend to be "Free Shipping" items that actually have the shipping bundled into the price. We all know there's no such thing as "Free Shipping". In this case, the LD is retailing for 11.43, whereas on his website it's 6.49. That means that while it might be a marginally better price buying 1, the more you buy, the worse deal Amazon is. There's no bundled shipping (or, they are bundling shipping, but they're not passing those shipping savings on to the consumer). Amazon's pricing scheme works better on big ticket items, because the shipping is a smaller portion of the overall cost of the items.
FBA makes the most sense if you're selling massive quantities. There's a certain tipping point where the cost of fulfilling via Amazon is cheaper than doing it yourself. But on a small scale it's definitely cheaper to do it yourself.
One other thing- Amazon now offers an alternative payment method, Amazon Payments, similar to paypal. That is something I'm using now, and I love it. It's just slightly more expensive in terms of Credit Card Processing fees (3%), but it's far cheaper than selling on amazon, and customers can use saved shipping info, Amazon gift cards, etc.