I bought these new from a UK ebay shop (kmagencies) for £22.50 which is US $35.95 or €26.56. Price included next day live tracked delivery with the delivery timed accurately to within an hour slot so if you're in the UK and want a pair of these this has to be both the cheapest and most convenient deal you will find.
I have had some bad luck with full size headphones:
My Sennheiser HD 500 died after about 10 years.
Pros: Good isolation. Detachable cable. Can sound very good. Comfortable. Huge value.
Cons: Unmodified the sound is intolerably harsh and piercing.
Having received two other Superlux headphones in the past I wasn't expecting much outside of a no frills cardboard box. While I wasn't completely blown away, Superlux definitely took some notes from other companies and made the packaging much more appealing than the 668b or the 651. The 661 come in black box with red sides, what's interesting though is that on the front right half the 661 are exposed by a plastic window.
Excerpt: Les presento una de las adquisiciones de los últimos años con la que más contento estoy, los cascos Superlux HD 661 (color negro en mi caso). Son unos magníficos cascos con los que aparte de poder disfrutar de escuchar tu música con tranquilidad, también podras utilizarlos en un ámbito semi-profesional, ya que son ideales para tus comienzos como dj, o en caso de que te guste tocar algun instrumento (batería, guitarra, bajo...