Why are xbox 360 wireless network adapters kinda pricey

Gamestop sells them for $14.99 and every time I bid on some on ebay, they end up going for 16,17,18+ dollars with shipping which seems like a little bit too much. Anyways I am looking for one so I'll keep hoping I'll find one at goodwill for hopefully cheaper or at a yard sale. In the meantime I am also looking for a 2nd generation lexus gs 300