$20 because of the cold packs and overnight shipping to ensure that it's still frozen once you get it. Unless you're ordering in LARGE quantities, or very specialized foods, local purchase is still the way to go.
What are your trying to buy that can't be purchased locally?
I'm just curious. I wanted to buy some cyclopeez but none of the stores around here carry it. So I followed a link that was provided in Advanced Aquarist to the Manufacturers website. I emailed the company and eventually got them together with one of my LFS and he now carries it. And they sent a complimintary package for me as my finders fee!