I recently tried to see how much Pokemon Heart Gold and Pokemon Platinum were, so I could deduce whether or not it was reasonable to ask for one for Xmas. Wanted to play my favourite Generation without ROM hacks. But brand new/unused game of HeartGold for £35-40 (more than when it was new on shelves) and new Platinum go for £85-£100 new. Why? Neither of these are particularly rare as far as I can work out, and as much as I love them they're not exactly golden age. They're also just DS games.
Note: I'm not asking where I can buy for cheaper, I know that already. I just wanted to know why they're so expensive.