Lowest price for used (with minor cosmetic imperfection) on Amazon Warehouse is $343 + tax. I am asking $325 shipped (to Cont US) for a near new condition unit. Local pickup for $300. Paypal add 3%. As one of four headphones I own, it has very low hours of use: 9/10 is conservative rating.
Compared to HD 600/650, I find the HD 700 to be distinctly more resolving. In particular, I like the "speedier" presentation of the 700. I think the "Truly Excite Your Ears" description by Sennheiser is spot on. It is also undoubtedly the most comfortable of the Sennheiser lot, and is driven easily without the need for exotic amps.
I just upgraded to the HD 800, hence the sale. Check my feedback and buy with confidence.