I wish there was a Costco where I live. I usually get them from Wal-mart, either the actual store or Wal-mart.com (sometimes they're cheaper online for some reason.) But for both seasons of Alias, BestBuy cheaper, oddly enough.
I only have Seasons 1-3 of Buffy and Season 1 of Angel. I'm so broke...Actually, I shouldn't be, but one of my family members has been secretly taking money out of my check account, and now it's empty. So, looks like it'll be a while before I can revisit Sunnydale.