That's because their funding model is different.

I had dismissed that title out of hand, precisely because of the prices, but recently discovered that's only for people who want the option of directly contributing to the development. The finished title will apparently have all ships for in-game credit purchase, just like ED does.
With ED, it's essentially been released and is getting more refined along the way. It looks like SC is still effectively in limited beta-release, but with greater direct financial input for people who believe in the product's end goal.
Both models are valid. I'd like both to succeed, because accessible space/flight combat simulators have been in limbo for ages and competition breeds invention. Eventually, I might even get SC, too (if for no other reason than it looks like it'll implement a proper military career, whereas ED seemingly won't). Right now, I like ED's attempt at realism and am very interested to see how it will go about stuff like atmospheric flight/landings.
Also, I kind of like SC's ship designs a little more... At least, until the Federal Corvette is finally here.