they've already sold out of the four-day badges that include access to preview night.
THAT IS NOT A TYPO. They have sold out of their alloted 4 Day + Preview Night badges. I can't even imagine-- the convention isn't for more than NINE MONTHS from now! And the preview night badges weren't cheap, either-- $100. The four-day badges without preview night are still available, but don't go thinkin' that you'll get any kind of discount...it's STILL $100. Insanity.
However, they haven't opened up any other badges at the moment, so if you're going to try for a single day badge (or several), you'll want to be keeping a very close eye on this page for when they come available...lest they sell out of THOSE insanely quickly, too. Yeesh!
Dear San Diego: please hurry up and get bigger. I don't think there's a bigger option for SDCC in the US at the moment, and they NEED to be able to let in more people. Good grief.