Currently, the Dan Clark Audio ÆON RT headphones, both open and closed, are on sale for $399.99. Regular price is $499.99.
DROP has the Drop + Dan Clark Audio Aeon Closed X and Open X for $499 and $449, respectively. So you save $50 or $100 depending on the model and can choose which cable you want included if you were debating between the RT and X models.