I'm going to buy this sennheiser cx 400 ii from ebay http://www.ebay.com/itm/CX-400-II-BLACK-Precision-In-Ea...
it's only 22 $ (+6$ for shipping) and it's coming from a top rated seller.
i'm not sure about it's authenticity
AM I GOING TO BUY A FAKE SENNHEISER EARBUD?
P.S. I think 20-30 $ is the current list price for sennheiser cx 400 ii on ebay