Well it's people on ebay who went to SDCC, selling the goodie bag, comic book, etc. It's not like you're buying direct from FOX/Sega/Dark Horse/whatever.
I happened to bid on an auction that had both the bag and the comic, and won for about $10 shipped. There's a bunch of other comparable auctions for similar prices, too. Just do a search for "SDCC Isolation" or something similar and it'll bring up a bunch of stuff.