I remember selling someone a hat through PayPay for Diablo 2 LOD for around $300. It was a very rare unique that they subsequently nerfed. Paid for the game, the expansion pack, and likely many months of service from my ISP
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Personally I likely won't buy any items for D3, but what is the difference between this and downloadable content you pay for -- outfits for your xbox 360 avatar, extra cars for Forza, extra maps for COD, etc... Lot of games have micropurchases -- especially phone and tablet games. I don't think this is much different when the price is like $1 or $3 -- but $250? wow.