You are looking at what usually ends up being the most valuable SDCC exclusive of the entire 'con each year, and you know what? They're actually free!
LEGO has some of the most fanatical and wealthiest collectors in all the world. And there are literally collectors all over the world. Combine that with the fact that these figures are very limited and very hard to obtain and you've got the makings of some insanely expensive figure on the after-market. Most go for over $100 with some going as high as $300-- and again, these are free at the show.
But don't go bum-rushing LEGO's booth thinking that you're going to come away from the 'con a rich man. There are things you must do to get these figures. Lines you must wait in. And 99.9% of the people who hope to get one don't.
In past years, you has to stand in a long line to either get your badge scanned or pull a raffle ticket and then come back later to see who won the raffle, thus winning a figure. Not all the figures-- just one. The figure for that particular day.
So, now you begin to see why these go for so much. Not only are they limited, but the chances of getting one is slim. But, hey, someone's gotta win, right! See you there!