eBay:
Sennheiser HD 515 -- $34
Sennheiser HD 525 -- $40
Sennheiser HD 580 -- $160
We have a local store nearby called "Unclaimed Baggage". All the merchandise in the store is literally that, unclaimed or lost baggage and luggage from airlines all over the world. When you fly, if your luggage gets lost, chances are, it ends up in Scottsboro, Alabama (U.S) at this store. They have tons of stuff !! I usually cruise by there once a month or so.
They have headphones coming out of their arse !!! They have one whole wall of cheap headphones. The really nice, expensive ones are behind the counter but they will get them out for you to try. Average prices are about 30% - 50% of retail. Some recent finds:
Audio Technica M50s -- $50
Sennheiser HD 280 pro -- $48
Bose AE2 -- $55
Klipsh Image Ones -- $22
Denon AH-NC732s -- $15
Ultrasone HiFi 450s -- $9
They regularly have tons of headphones (lower end, mostly on ear, Sonys, Panasonics, Sennheiser, JVCs, Audio Technica, Skullcandy, and others) on the cheap headphones wall for less than $10.00. They put out new merchandise daily so it is kind of the luck of the draw when you get there. Sometimes you can find bargains,other times, its just picked over junk.